Troubleshooting and Repair of
Consumer Electronic Equipment

Preface

Author and Copyright

Author: Samuel M. Goldwasser

For contact info, please see the Sci.Electronics.Repair FAQ Email Links Page.

Copyright © 1994-2007
All Rights Reserved

Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

1.This notice is included in its entirety at the beginning.
2.There is no charge except to cover the costs of copying.

DISCLAIMER

Introduction

Getting Into Troubleshooting

Mostly, you will learn by doing. However, you do need to prepare.

There are many schools dedicated to electronics repair. Some of these are quite good. Many are not. This document, however, is written from the perspective of the motivated do-it-yourselfer, hobbiest, and tinkerer.

The Repair FAQs usually list suggested references for each area. Your local public or university library will probably have some of these or other repair oriented electronics books.

Above all read and understand the document: Safety Guidelines for High Voltage and/or Line Powered Equipment. Your life may depend on it. That fabulous large screen won't be of much use to you if you are dead.

Collect broken electronics and appliances from your friends, relatives, the dump, garage sales and flea markets, etc. Start on those that have been written off - you will screw up at first. We all did. As times passes, your batting average will improve. It may not happen overnight but it will happen if you apply yourself. There will be many relatively easy successes but the 'tough dogs' may make up for these triumphs. Don't let them get to you - not everything can be repaired. Sometimes, the basic design is flawed or someone before you messed up royally. Troubleshooting is like being a detective but at least the device is generally not out to deceive you.

Experience will be your most useful companion.

If you go into the profession, you will obtain or have access to a variety of tech tips databases. These are an excellent investment where the saying: 'time-is-money' rules. However, to learn, you need to develop a general troubleshooting approach - a logical, methodical, method of narrowing down the problem. A tech tip database might suggest: 'Replace C536' for a particular symptom. This is good advice for a specific problem on one model. However, what you really want to understand is why C536 was the cause and how to pinpoint the culprit in general even if you don't have a service manual or schematic and your tech tip database doesn't have an entry for your sick TV or VCR.

While schematics are nice, you won't always have them or be able to justify the purchase for a one-of repair. Therefore, in many cases, some reverse engineering will be necessary. The time will be well spent since even if you don't see another instance of the same model in your entire lifetime, you will have learned something in the process that can be applied to other equipment problems.

As always, when you get stuck, the sci.electronics.repair newsgroup will still exist!

Happy repairing!

Comments on How to Learn Repair

Here's how I see it:

By all means, do what you can to understand basic principles first. Your success will be much more likely when you understand how a device works. If you can, read Electronics Now and Popular Electronics, as well as Nuts and Volts (http://www.nutsvolts.com/). Also have a look at the Radio Amateur's Handbook.

These periodicals are not carefully edited, unfortunately, and now and then things get into print that are simply wrong or misleading, but they are still useful; I learned quite a bit from their predecessors (Radio Craft and Radio News!).

I can't speak firsthand, but it might be a very good idea to become (eventually) a Certified Electronic Technician. Look up the I.S.C.E.T.

Hearsay and folklore sometimes indicate that you should replace a given part when certain symptoms occur, and in the case of frequent failures of such parts, this information might even be true. But that's no way to become a competent technician.

My personal take is that you have to know when to 'let go' of an hypothesis about what the cause of the trouble is. A tech. who persists beyond a certain point in his belief that such-and-such is causing the problem is stuck and spinning his wheels. (I'm sexist; I think women are far less likely to get stuck this way! I think it's a male trait. :)

Troubleshooting is a special field of knowledge and has its own special outlook on things. The device did work, after all.

Production testing and troubleshooting is different; you are likely to be the first person to apply power to a device, and the device has never worked before. If the assemblers aren't giving you excellent quality, you can have some remarkably-bizarre symptoms with a poorly laid-out board from solder shorts, for instance.

A variable toroidal autotransformer (universally known by what used to be a General Radio trade-name, Variac) is priceless for troubleshooting circuits that handle any amount of power and which are powered by the AC line. (Not all devices function at all at, say, half of rated AC input; I work on a poorly-designed amplifier that draws many amps at something like 70 volts with no signal and no load. Unfortunately, Variacs and their equivalents are horribly expensive, at least from some sources! If you get a used one, see that the contact area of the winding is undamaged; you might need to remove a knob and some covers to see it. If the knob is stiff, try some contact/control cleaner/lube; it did wonders for mine!

Learn how to operate a 'scope, and learn why you see what you do. I suspect that some techs are not too well-informed about what goes on inside a 'scope; learn from reliable sources!

Learn to use a digital multimeter, and an analog one as well; the latter is easily damaged if you don't know what you're doing, but it's a great trend indicator.

Learn to use a function generator, and use the triangle output as well! Nothing like a triangle to show a wee bit of clipping or limiting in an amplifier...

Learn how to solder! Solder is not an adhesive; it's a metallurgical bond, according to some sources I trust. It just about has to be with gold, at least! If you *really* want to learn soldering, NASA has developed training courses that will make you a disgustingly good solderer.

(From: Phillip R. Cline (pcline@iquest.net).)

I used to repair consumer electronics from VERY high end stereos down to lowly boom boxes. When repairing stereos there is no substitute for good troubleshooting techniques which come from empirical means. Good knowledge of circuit functions helps a great deal. VCRs are almost always a mechanical problem (70% or more in my experience). Audio stuff can be destroyed by the user and often times the design is just plain crap. All low and mid-fi Japanese stuff made within the last ten years isn't worth a crap from a design standpoint. Even a lot of the high-end stuff is junk. They have 71 volt rated caps running at 69 volts etc.... US and most European stuff is way better designed! There are exceptions. I once saw a Philips amp that had a transformer for the power amp supply that wasn't centertapped yet the supply was bipolar. They just rectified and filtered the AC with series caps and the common was the point they were connected to each other. This is fine if you rate the caps at more voltage than the power supply can deliver but these were rated at just over half the total voltage of the supply from rail to rail. One cap shorted and the other one exploded and launched the can sideways across the component side of the amp PC board. This basically did a nice job of depopulating the board along the ballistic path of the cap's can. I laughed for a good while after seeing this.

I gave up repairing stuff when the customers asked, and rightly so, why it costs $80 to fix something that costs $100 new. The OEM parts cost on some stuff was intended to make the customer go buy a new unit instead of repairing the old one. This basically made most of the stuff disposable.

My background was and still is as an electronic hobbiest so the theory of operation was not a big deal and circuit function wasn't either. I have a brother that was the person from whom I learned a great deal of what I know now about electronics.

Soldering ability cannot be overstressed in importance especially with SMT being very common nowadays. As for the guys that seem to be ripping you off in their pricing, they could be gouging you but most often the overhead in the shop and their cost on parts is the most likely cause of high pricing. While labor might seem high a great deal of repair can be accomplished in an hour by a competent technician and some shops have a flat rate for a given repair. This can work to the benefit of the shop sometimes and to the customer sometimes. Our shop was this way. We had the lowest pricing in town(Indianapolis) and the customers still bitched. Sometimes they would take their units after we gave them the price for labor and a estimate of parts cost. We didn't charge for estimates. They would storm out only to come back with their tail between their legs in a few days after checking around for labor charges elsewhere. Depending on their attitude we might go ahead with the repair. Often times we would decline by telling the customer that the other shops may have done something while checking the unit out.(This depended on the shop that the customer took the unit to.) Some of these places had some real winners for techs!! We really didn't feel like undoing some yoyo's handiwork just to get the unit back to it's original nonworking state!

An EE in electronics is useless by itself and will cause a lot of undue troubleshooting to the beginning tech. They will overlook the obvious easy stuff for some possible but unlikely fault. A few years of repairs under their belt though and they can find the most difficult electronic problems with relative ease.

The best way to become proficient is with hands-on training under an experienced tech. A good overall background in electronics doesn't hurt either.

(From: Michael Black (blackm00@CAM.ORG).)

I think one of the problems of home repair is fear. If you're willing to spend the money to have something repaired, then you may think that if you fiddled with it you may make it worse. On the other hand, if you are about to throw something out because it doesn't work, you have nothing to lose by playing around with it and trying to fix it. Or find some stuff other people have thrown out, and start with that.

You may not fix it, but your willingness to open the cover allows you a familiarity that you won't get from a book. You de-mistify the equipment, and by actually adjusting things and seeing the results, you will learn.

I picked up a VCR for cheap at a garage sale this past summer. I was buying it as a tuner for use with a monitor. The guy said it "must be the power supply because it keeps turning off". Actually, it kept turning off because the mechanics weren't working properly. By moving the parts by hand, I saw how they were supposed to work. With the first hand experience, the S.E.R FAQ made more sense than if I'd just read it first, and so did a book on VCR repair that I took out of the library. I saw that the belts needed replacing because I'd figured out how things were supposed to work, and saw that they weren't working that way.

(From: Malcolm MacArthur (malcolmm@rustic-place.demon.co.uk).)

I have two years' of an Electronic Engineering degree behind me (I gave up on the degree and became a computer programmer. ;) It has been little, if any, help. What you really need is experience... which you'll only gain by fiddling with things. I've been doing repairs since about age 13. After twelve years, I now have a fair success rate, but those first few years were not easy. Best thing to do is get hold of old equipment and just have a go with it (Beware of CRTs, though ;). Be warned, you may break quite a lot of stuff initially! But as the others have said, most of the problems are due to mechanical failures (including dry solder joints).

Tall repair stories time:

• The IDE hard drive, given free, with two broken pins. Fixed with bits of bent paper clip soldered in place of the original connectors.

• The record player which wouldn't play at the right speed, and there wasn't enough adjustment in the pot. Fix: cover belt spindle in Araldite, leave to harden, machine down with scalpel.

• The VCR which wouldn't play. Roughened up drive tire with sandpaper, did same to spindles, worked a treat. Still working fine after 3 years. :)

• Another VCR, rejected by a repair shop as uneconomical to repair, and given back to my friend's aunt. Took it apart. found nothing wrong, cleaned it, reassembled. Still working fine (I have no idea what the "fault" the shop found was).

• A computer monitor with incorrect colour balance. Fixed by adjusting the guns at the back WITHOUT an insulated screwdriver (Hairy!). I didn't have one, so used a normal screwdriver taped with insulating tape to a (dry) 1 ft. wooden spoon. Oh, because of poor design, the CRT kept threatening to impact with the mainboard when I had the back off, so I had to hold it at the front with my other hand. Visions of 25,000 V going straight through my chest made it all a bit scary. :)

• First ever repair (this is true!): taught my mother how to wire up a household (e.g. at power meter) fuse because I'd watched my Dad do it (he's good at this sort of thing as well. :) Age? Five.

• A TV with a broken tuner, had been to a repair shop twice, they'd given up on it. Received it for free, found out the composite video in worked fine, so ran 20 ft. of cable to a spare video downstairs (there was no aerial in my room, see). Must fix that tuner sometime...

• A CDROM drive which couldn't read near the edge of some discs. Disassembled whole unit, (eventually) reassembled it, found out that I was the spring which holds the CD down. Fixed by plugging into computer, running a cdrom and wiggling the spring with my finger until I felt the least vibration. Still works fine, although I am replacing it soon with a faster unit.

• The dropped TV with a crack at the corner of the mainboard. Repaired all the cracks by patching with wire, TV nearly blew up in my face (hence, beware of CRTs). Thank goodness for the fuses... this little incident put me off repairing TVs for over a year. It was eventually chucked, a failure.

Have fun.

THE Question: To Repair or Not to Repair

"Why bother with repair of VCRs (or anything else) when I can buy a new model for $79.95?"

Actually, I've seen prices as low as $39.95 for a promotion (but not requiring the purchase of anything else)!

or:

"This stuff may have been useful 5 years ago but now some/much of the material doesn't apply to newer VCRs."

While both of these deal with VCRs, it should be understood that it applies equally well to much other consumer electronics.

Depending on your background and interests, these statements may have some validity. Thus, the need for some objective (if possible) way of making a decision as to whether to bother at all, and whether to attempt the repair yourself.

So, when does it make sense to attempt *any* repair yourself rather than to toss the item in the trash or take it to a professional? People do this sort of stuff for several reasons:

1. For the challenge and rewards associated with success.

2. To save money.

3. Because they like a particular set of features or the controls or the styling of the equipment and don't want anything new!

4. To avoid cluttering land-fills.

It's quite difficult to suggest an approach in deciding when something is worth repairing. You have to decide how much the equipment is worth to *you* in terms of monetary, sentimental, or other value; how much time you are willing to put into a repair; and whether the failure represents a good excuse to upgrade! To what extent each of the factors is significant will also be determined by how much you enjoy troubleshooting and tinkering. If you'd rather be doing something else or keep thinking about all the time you are spending on this rather than something you can charge for, perhaps you should be doing that something else.

However, it is easier to identify specific situations where equipment probably *isn't* worth attempting to repair on your own (or possibly at all):

1. Serious damage due to water (especially salt water), fire or smoke. Even if the obvious faults can be found and corrected, there are likely to be latent failures just waiting to strike in a few weeks or months.

2. Lightning strike. Lightning is like the 900 pound gorilla - it can go anywhere it wants. Even if you can repair the obvious damage and get the equipment working, there could be hidden problems waiting to appear at a later time due to components that aren't totally fried but just weakened.

3. Extremely high electrical power surge like a 13,000 V feeder line falling across the 115 V wiring to your house. Similar comments as lightning apply.

Where any of these are covered by insurance, that is the best option where the settlement is at all reasonable. If the insurance company allows you to keep the damaged equipment, there is nothing to stop you from attempting repairs as a challenge - you may get lucky. But, it could also be a long drawn out and expensive frustration.

4. Serious physical damage, especially for equipment with mechanical parts like VCRs. It may be impossible to replace broken parts. Twisted metal can be straightened but there is a good chance there will still be erratic misbehavior.

5. Equipment where prior attempts at repair may have resulted in an undetermined number of new unidentified problems. At least when something breaks on its own, your only opposition is the device itself. But, if another person attempts a repair and they are a novice or just plain incompetent, the dumpster may be the best solution.

6. Equipment with known design or manufacturing problems. When we undertake a repair, one assumption that is usually made is that the equipment originally worked correctly and/or that the fault isn't something that was designed in before the name went on. :) For most things, this is a valid assumption. Even the famous RCA/GE/Proscan and Sony TV solder problems, while no doubt resulting in 100s of thousands of sets ending up in the trash, are repairable with modest effort at low cost. And, the result is a well performing reliable TV. However, some computer monitors may die when fed a particular scan rate or during boot when mated with a particular video card - a design flaw which may not have a (known) solution.

7. Newer throw-aways. I can pretty much guarantee that a $39.95 VCR isn't worth any effort unless the problem is obvious. This junk is built as cheaply as possible with a lot of plastic parts, no thought given to access for testing or repair, and with attention only to the short term bottom line. There has been no miraculous invention to reduce construction cost of the relatively complex VCR mechanism - it comes out of reliability.

8. Equipment like cell phones, pagers, and other modern wireless devices as well as cordless phones; PC mainboards, peripheral boards, and disk drives; TV set-top, cable boxes, satellite receivers, etc. It is essentially impossible to obtain service information on any of these so unless the problem is an obvious broken connector or broken trace on the printed circuit board, or possibly a dead power supply, forget it. You don't have the documentation, test equipment, rework equipment, or any chance of buying many of the repair parts in any case.

9. Any situation where safety would be compromised by your repair. For example, attempting to reconstruct a smashed microwave oven door or jerryrigging a flyback transformer that has serious arcing. Where items (1) to (3) are involved, one must very carefully inspect for any possible safety related damage (like charred insulation in hidden areas) that may not have affected operation.

10. If you really don't know what you are doing, leave it to a professional! Not only is it dangerous to be poking around inside many types of equipment if you don't even know what not to touch, there is a strong likelihood that such attempts will cause additional, possibly fatal damage to the circuitry. Even if the equipment can be repaired, the ultimate cost will end up be much greater than had you not done anything in the first place, both in terms of labor (troubleshooting and repair) and parts. If you can't justify a professional repair, just set it aside until you have gained more experience and can deal with the equipment safely (for you and it).

11. Finally, don't attempt to repair a piece of equipment for which you are not equipped in the tools or test equipment department. Attempting to remove a part from a multilayer printed circuit board without proper desoldering equipment will just make an unsalvageable mess. Guessing at a replacement part ("I heard that the flyback transformer is a likely cause for a dead monitor.") will just end up being frustrating and expensive (unless you've won the Lottery recently in which case maybe your luck is still holding).

In the good old days when life and electronics were simpler and you could count the total number of transistors in a TV on your hands and feet, service information was included with the equipment or was readily available either from the manufacturer or Sams Technical Publishing (formerly Howard Sams) as Sams' Photofacts (no relation to me). There are still Sams' Photofacts for many TVs at least, but for anything else, obtaining schematics may be impossible or even if they are available, the cost may be excessive. Paying $100 for a mediocre copy of a service manual for a computer monitor that can be replaced for $250 may not be justified.

One way to get an idea of your chances of success for popular brands and models is to search the archives of the USENET newsgroup sci.electronics.repair via Google Groups (formerly Deja.com/Dejanews. There are other public USENET archives but even though this archive keeps changing its name, I see little reason to use others which may come and go and provide less reliable coverage.) Where others have experienced - and repaired - similar problems, your chances of success are greatly increased. Then, if you have detailed symptoms, asking for suggestions on that newsgroup may also be beneficial, especially if you have already done some initial testing. If, on the other hand, the consensus from the newsgroup is that your problem is hopeless, then you may be able to save a lot of time and frustration by giving up immediately (or at least postponing your efforts until you have more experience.

What about older equipment?:

The basic technology of TVs and VCRs hasn't changed significantly in 10 or 15 years. Yes, there are convenience features like "auto clock set" which are supposed to make life easier but often don't (if the station transmitting the clock information has their clocks set wrong or uses a feed from a source in a different time zone!). But as far as picture and sound quality, that VCR from 10 years ago will be just as good or better than one purchased today. Any, it will almost certainly be better constructed and more maintainable.

For example, Panasonic VCRs from the mid to late '80s were solid machines that could be kept in shape with a bit of periodic maintenance (cleaning, rubber parts replacement) and repair of known problems (failed electrolytic capacitors in the power supply after 10 years or so). One could not expect that $39.95 special to provide such service. If it lasts through the warranty period, you're probably ahead of the game. I'd still take a middle age Panasonic over any new low to medium priced model. And, even the high-end VCRs may be based on flimsy chassis.

Case studies:

Here are 4 examples of equipment that I did eventually repair but where serious consideration should have been given to the dumpster. The following can be found described in more detail at in the document: Sam's Repair Briefs/

1. GE TV dropped: (From: Repair Brief #69: GE Portable Color TV - Dropped.)

   This TV had taken a nose dive off of a 4 foot shelf onto an unknown surface. And, of course, someone had probably attempted to operate after this with possible additional damage. While the exterior didn't show any major abuse, it was obvious that there was severe trauma as soon as the back was removed. The main circuit board was broken near the (heavy) flyback transformer. Several dozen traces were severed including some to surface mount parts.

   A repair shop would be unlikely to want to tackle this for several reasons: (1) the obvious repairs to circuit board traces would take a couple hours at least, (2) there could be unseen damage to the CRT in form of a distorted shadow mask and this wouldn't be known until the circuit board was fixed, and (3) any repair might not catch everything so future problems could develop.

   As it turned out, the only damage was to the circuit board and after 2 or 3 hours of soldering - and then finding additional traces to solder - the set was fixed, and has continued to operate reliably for many years.

2. GE TV with 'rivlets': (From: Repair Brief #59: GE 13AC1504W Color TV - Dead (with Other Problems)).

   In the early 1980s, some brilliant manufacturing engineer working for GE decided that a good way to save money on circuit boards would be to use what were dubbed 'rivlets' instead of actual plated through holes to connect top and bottom. A rivlet is basically a rivet which, the theory goes, is then soldered to the copper traces. That's the theory. In practice, due to the thermal mass of the rivet, soldering was never reliable. And, as a result of thermal cycling, cracks developed between the rivet and traces over time. Problems ranged from a dead set to loss of color depending on which rivlet happened to be unhappy on any given day.

   Attempting to repair just the problem rivlets was impossible because as soon as you found a bad one and soldered it, another in its vicinity would decide to fail. The only approach that worked was to reheat every one that could be located using a soldering gun. Since there were many dozens of these on the circuit board, this took quite awhile and it was easy to miss some. In fact, the only truly reliable repair would be to remove the solder from each rivlet, snake a bare wire through it, and solder the wire directly to the traces top and bottom. This repair would also take a couple hours and likely be too expensive for a small TV, though if the same chassis were used on a 27 incher, might be worth it.

3. CD player restoration: (From: Repair Brief #10: Pioneer PD5100 CD Player Trashed).

   Here is a case of a piece of equipment being partially destroyed by previous repair attempts. The Pioneer PD5100 is a basic solid CD player but this one had broken parts in the loading mechanism and was in unknown operational condition. If it were taken to a repair shop, the response would probably be something along the lines of: "Well, that certainly looks like a CD player.". It simply wouldn't be worth the time and effort to repair what was obviously broken with the possibility of finding more serious electronic problems after that.

   I had nothing better to do (!!) so decided to attempt to restore it to something usable. After repairing the mechanical damage, there was indeed a servo problem which ultimate required the replacement of a motor driver chip - for which I got lucky. The player would read the disc directory but was unable to seek to any track, even #1. One of the chips was getting hot. So, I replaced it and after servo alignment, the play problems were cured. If that hadn't worked, there was probably little more I could have done. Very likely, the servo chip was the original problem and the previous repair attempt created the mechanical mess.

4. Sony TV with bad butchered soldering: (From: Repair Brief #81: Sony KV-19TR20 Color TV - No Reception).

   The final example is of a Sony TV that had the infamous tuner/IF box solder problems. This is normally a fairly easy repair, especially for this particular model where the IF box (which was faulty in this case) is readily accessible without taking the whole thing to bits. Once repaired, like the RCA/GE/Proscan TVs with similar solder problems, the result is a solid reliable TV. However, the friend of a friend who had attempted to replace it, apparently used a Weller soldering gun to do the fine soldering, leaving nearly every pad detached or missing. Fortunately, only the pads appeared to have suffered and after 20 minutes and several jumper wires, this one was healthy again.

Repairs for the novice:

It would be way too easy to poison your future outlook on servicing by attempting repairs multiple times and failing or making things worse.

Equipment that is good to learn on because there will likely be immediate or at least ultimate gratification might include: small appliances, power tools, remote controls, and basic audio equipment like tape decks and low power amplifiers (not big power amps!). And, while electronic troubleshooting of CD players and VCRs is definitely for the advanced course, they often have problems that can be easily remedied by a proper cleaning and/or general maintenance. Electronic problems are tough to diagnose but most are mechanical. Microwave ovens are generally easy to repair but due to the very serious safety issues, I'd suggest holding off on these unless you are experienced in dealing with high voltage high power equipment.

With reasonable care, PC troubleshooting involving basic swapping of components, can also be rewarding. But, don't expect to repair a mainboard with a peculiar failure of IRQ2 (unless you find a lockwasher that ate through to some PCB traces!).

Intermediate level troubleshooting and repair would add TVs since service information in the form of Sams' Photofacts is available for the majority of popular models. Video (not computer) monitors are also straightforward to deal with. And perhaps, audio amplifiers and receivers.

For those just starting out, there are some types of equipment to avoid (beyond those mentioned above). One in particular is modern computer monitors. With their wide scan rate range, microprocessor control, need for decent test equipment, dangerous voltages, and the general difficulty in obtaining service information, even professionals will stay away from many of these - particularly no-name or non-major brand models. Except for obvious problems like bad solder connections, a blown fuse (replace ONCE only, might have been a power surge), or the need for degaussing, they may not be worth the frustration, certainly not as your first project. TVs are not only much simpler than computer monitors, but as noted, complete service information is usually available.

If You Decide That You Don't Want to Bother Repairing Something

Don't just toss it in the trash. See if a local charity like the Salvation Army or Goodwill accepts broken appliances and electronics. They may have someone on staff who can perform at least simple repairs and then resell the item. Not only will this reduce clutter in the land fill, you may benefit on your taxes (and in the good deeds department). However, it really isn't proper to do this if you have already worked on the item and given up or reduced it to a pile of slag!

Smoking Around Electronic Equipment

If you still doubt the harmful effects of the chemical compounds in tobacco smoke on your health and that of others around you, whatever I say below probably won't matter and you may want to skip it since it may upset you. However, perhaps, you worry more about your fancy, costly, finely tuned electronic entertainment and computer equipment. In that case, read on.

The several hundred chemical compounds found in tobacco smoke have the following effects on electronic equipment. What isn't trapped in your lungs or in the lungs of those around you:

• coats the precision optics of CD and DVD players, CDROM and DVDROM drives, and other optical disc/k equipment AND the media they use.

• coats the read/write heads of floppy disk drives, Zip drives, tape drives, AND the media they use.

• coats the tape path of VCRs and audio decks including the audio, video, and control heads AND the cassettes and tape inside.

• coats mechanical parts and promotes the loss of lubrication in all equipment.

• may contribute to deterioration of plastic and rubber parts.

• coats the screens of TVs and monitors, display windows of VCRs and other devices, and the outside and inside of everything eventually resulting in ugly brown discoloration and a horrible stench.

The resulting film WILL eventually cause problems and is very difficult to remove. Damage done due to chemical action may require the replacement of costly parts. Increased maintenance will be needed or the equipment may simply fail before its time and not be worth fixing. Contamination will often find its way into critical places that are not accessible and to media which is irreplaceable.

When someone trys to get me to look at something that has been in a smoker's residence (I know because it will reek of stale tobacco smoke essence), my first inclination is to put it in a sealed bag to go out with the garbage. (I have been known to drop portable TVs directly into the nearest trash can under these circumstances.) If this isn't an option, my next objective is to get it evaluated and repaired or refused as quickly as possible. However, my concentration may not be at its peak for such equipment! It is a good thing that I don't need to do this for a living - I would have to refuse service to a good portion of the world's population :-(.

So, now you have a few more reasons to give up the stupid, disgusting, filthy, obnoxious, inconsiderate of others, costly, dangerous, killer habit!

Sorry, end of editorial. :-)

General Safety Considerations

• Electrical shock hazard from TV, computer and other video monitors, microwave ovens, the switchmode power supplies in some VCRs and computer peripherals, electronic flash units, some parts of audio equipment, hand and stationary power tools, large appliances, and even many small line powered appliances.

• Mechanical hazards from the moving parts of various appliances, computer peripherals, hand and stationary power tools, and especially gasoline powered yard equipment.

• Risk of CRT implosion from equipment using large CRTs.

• Vision hazards from the lasers in CD players and CDROM drives, DVD players and DVDROM drives, other optical data storage devices, and laser disc players.

See the document: Safety Guidelines for High Voltage and/or Line Powered Equipment for general safety information.

See the SAFETY sections of the documents dealing with your equipment for additional safety information for your equipment.

Basic Troubleshooting

Some of My Rules of Troubleshooting

1. Safety first - know the hazards associated with the equipment you are troubleshooting. Take all safety precautions. Expect the unexpected. Take your time.

2. Always think 'what if'. This applies both to the analytic procedures as well as to precautions with respect to probing the equipment. When probing, insulate all but the last 1/8" of the probe tip to prevent costly shorts. (If I had a nickel for every time I have been screwed not following this advice...)

3. Learn from your mistakes. We all make mistakes - some of them can be quite costly. A simple problem can turn into an expensive one due to a slip of the probe or being over eager to try something before thinking it through. While stating that your experience in these endeavors is measured by the number of scars you have may be stretching the point, expect to screwup - we all can point to that disaster due to inexperience or carelessness. Just make it a point not to make the same mistake again.

4. Don't start with the electronic test equipment, start with some analytical thinking. Many problems associated with consumer electronic equipment do not require a schematic (though one may be useful). The majority of problems with VCRs, CD players, tape decks, and answering machines, are mechanical and can be dealt with using nothing more than a good set of precision hand tools; some alcohol, degreaser, contact cleaner, light oil and grease; and your powers of observation (and a little experience). Your built in senses and that stuff between your ears represents the most important test equipment you have.

5. If you get stuck, sleep on it. Sometimes, just letting the problem bounce around in your head will lead to a different more successful approach or solution. Don't work when you are really tired - it is both dangerous and mostly non-productive (or possibly destructive).

6. Many problems have simple solutions. Don't immediately assume that your problem is some combination of esoteric complex convoluted failures. For a TV, it may just be a bad connection or failed diode. For a VCR, it may just be a bad belt or idler tire - or an experiment in rock placement by your 3-year old. For a CD player, a dirty lens or need for lubrication. Try to remember that the problems with the most catastrophic impact on operation - a dead TV or a VCR that eats tapes - usually have the simplest solutions. The kind of problems we would like to avoid at all costs are the ones that are intermittent or difficult to reproduce: subtle color noise, the occasional interference, or the dreaded horizontal output transistor blowing out every 3 months syndrome.

7. Whenever possible, try to substitute a working unit. With modular systems like component stereos and computers, narrowing down a problem to a single unit should be the first priority. This is usually safe to do in such cases and will quickly identify which unit needs work. This same principle applies at the electronic or mechanical parts level. Note that there is the possibility of damaging the known good part by putting it into a non-working device or vice versa. This risk is most likely with the power circuitry in amplifiers, TVs and monitors, power supplies, etc. With appropriate precautions (like the series light bulb) the risk can be minimized.

8. Don't blindly trust your instruments. If your get readings that don't make sense, you may be using your equipment in a way which is confusing it. DMMs are not good at checking semiconductors in-circuit or the power transistor you are testing may have a built in damper diode and/or base resistor. Your scope may be picking up interference which is swamping the low level signal you are searching for (TVs and Monitors, or low level circuits in VCRs and CD players). Your frequency counter may be double triggering due to noise or imperfect signal shape.

9. Realize that coincidences do happen but are relatively rare. Usually, there is a common cause. For example, if a TV has no vertical deflection and no picture, it is much more likely that a common power supply output has failed than for parts in both the deflection and video subsystems to be bad. In other words, first look for a common root cause rather than trying to locate bad parts in separate circuits.

   Exceptions include lightning, power surge, dropped, water, or previous repair person damaged equipment. However, multiple electrolytic capacitors in older equipment may be degrading resulting in failures of unrelated circuits. Determine if all the problems you are troubleshooting have just appeared - see below. It is very common to be given a device to repair which has now died totally but prior to this had some behavior which you consider marginal but that was not noticed by the owner.

10. Confirm the problem before diving into the repair. It is amazing how many complaints turn out to be impossible to reproduce or are simple cockpit error. It also makes sense to identify exactly what is and is not working so that you will know whether some fault that just appeared was actually a preexisting problem or was caused by your poking. Try to get as much information as possible about the problem from the owner. If you are the owner, try to reconstruct the exact sequence of events that led to the failure. For example, did the TV just not work when turned on or were there some preliminary symptoms like a jittery or squished picture prior to total failure? Did the problem come and go before finally staying bad for good?

11. Get used to the idea of working without a schematic. While service info for TVs is nearly always available in the form of Sams' Photofacts, this is hardly ever true of other types of equipment. Sams VCRfacts exist for less than 10 percent of VCR models and only the older ones include anything beyond (obvious) mechanical information. While a service manual may be available from the manufacturer of your equipment or another Sams-like source, it may not include the information you really need. Furthermore, there may be no way to justify the cost for a one time repair. With a basic understanding of how the equipment works, many problems can be dealt with without a schematic. Not every one but quite a few.

12. Whenever working on precision equipment, make copious notes and diagrams. You will be eternally grateful when the time comes to reassemble the unit. Most connectors are keyed against incorrect insertion or interchange of cables, but not always. Apparently identical screws may be of differing lengths or have slightly different thread types. Little parts may fit in more than one place or orientation. Etc. Etc.

13. Pill bottles, film canisters, and plastic ice cube trays come in handy for sorting and storing screws and other small parts after disassembly. This is particularly true if you have repairs on multiple pieces of equipment under way simultaneously.

14. Select a work area which is wide open, well lighted, and where dropped parts can be located - not on a deep pile shag rug. The best location will also be relatively dust free and allow you to suspend your troubleshooting to eat or sleep or think without having to pile everything into a cardboard box for storage.

15. Understand the risk of ESD - Electro-Static Discharge. Some components (like ICs) in solid state electronic devices are vulnerable to ESD. There is no need to go overboard but taking reasonable precautions such as getting into the habit of touching a **safe** ground point first.

    WARNING: even with an isolation transformer, a live chassis should **not** be considered a safe ground point. This applies mostly to TVs, computer and video monitors, some AC operated strobe lights, and other line connected devices. You shouldn't be touching components with the device powered and plugged in (at least, not until you really know what you are doing!). Once unplugged, sheet metal shields or other ground points should be safe and effective.

Some Quick Tips or Rules of Thumb

• Problems that are erratic or intermittent - that come and go suddenly - are almost always due to bad connections - cold solder joints or internal or external connectors that need to be cleaned and reseated. It is amazing what a large percentage of common problems fall into the category.

  Pay particular attention to areas of the circuit board where there are large and/or high power components, connectors, or evidence of discoloration or actual charring due to excessive heat. Your eyeballs, a bright light, and magnifier will be the most useful test equipment for this purpose!

• Problems that change gradually - usually they decrease or disappear - as the equipment warms up are often due to dried up electrolytic capacitors.

  While capacitors will occasionally leak making diagnosis easy, in most cases, there are no obvious signs of failure. (Note: Don't be misled into thinking that the adhesive often used to anchor large capacitors and other components to the circuit board is leakage.) The most useful testing device for electrolytic capacitors is an ESR meter. However, heating suspect caps with a hair dryer may get the equipment going for the purposes of making a diagnosis. See the document: Capacitor Testing, Safe Discharging and Other Related Information.

• Problems that result in a totally dead unit or affect multiple functions are generally power supply related. These are usually easy to fix.

  Common failure items are the large hybrid power regulator ICs used in many VCRs and TVs, diodes and transistors, and remarkably - high value resistors that open up.

• Catastrophic failures often result in burnt, scorched, cracked, exploded, or melted components, or similar catastrophic consequences. However, some components run hot by design and slight discoloration on the circuit board in their vicinity, while not desirable, may be normal.

  Use your senses of sight and smell for the preliminary search for such evidence.

• Listen for signs of arcing or corona - snapping or sizzling sounds. A component on the brink of failing due to overheating may provide similar audible clues.

  Some discharge sounds are normal for a TV or monitor when powered on or off and occasional sounds of thermal expansion are nothing to worry about. The flyback, yoke, or other (usually) magnetic component may also emit a buzz or while constantly or intermittently without any other symptoms or implication of impending doom. However, repeated loud snaps or a sizzling sounds accompanied by the smell of ozone should be dealt with immediately since they can lead to more serious and expensive consequences.

• Most VCR problems are mechanical in nature. Worn or deteriorated rubber parts, gummed up lubrication, or abuse (bad tapes or toy or penut butter and jelly sandwich storage.).

  For any problem but a totally dead VCR, a check should be made for dirty or worn mechanical parts before even thinking about electronic problems or trying to locate a schematic - especially if the unit hasn't been cleaned in a few years.

• Many CD player problems are mechanical - dirty lens, worn or oily drawer belts, dirt/gummed up grease on sled tracks/gears, bad/partially shorted spindle or sled motor. Power problems with portables seem to be common as well. No matter what the symptoms, always make it a habit to clean the lens first - many peculiar failure modes are simply due to a dirty lens. Actual laser failure is relatively uncommon despite what the typical service shop may claim. CD players are also remarkably robust. Optical alignment should never be needed under normal conditions of operation.

• TV and monitor problems are very often power supply or deflection related. These tend to have obvious causes - blown posistor, rectifier diodes, filter capacitor, HOT, or chopper. Flyback with shorted windings or shorts between windings or in the voltage multiplier (if used) or screen/focus divider network are also common. Where the HOT or chopper is involved, operation should be observed after the repair as components in the vicinity may cause the new parts to fail. HOTs should generally not run hot. If they do, check for weak drive, excess B+, etc.

• Microwave oven problems are almost always power related. Faulty components in the microwave generator - magnetron, HV diode, HV capacitor, HV transformer - are relatively easy to identify. Sometimes, components on the primary side can cause baffling symptoms like the misaligned interlock switches that blow fuses or the weak triac that causes the oven to blow the main fuse only when the cycle *ends*. Control problems may be due to a spill in the touchpad, dried up electrolytic capacitors in the low voltage power supply, or failure confused state due to a power surge.

• Ink-jet printers are extremely reliable electrically. Look for simple problems such as caked ink in the 'service station' area, misaligned print-head contacts, or a nearly empty cartridge when erratic printing problems develop.

• Laser printers tend to develop problems in the fuser, scanner, or power control modules. These are often simple like a burned out lamp, bad motor, or bad connections.

• Turntables or record changer problems are very likely to be due to gummed up grease.

• Problems with audio tape decks like VCRs are mostly mechanical. Similar solutions apply. Where one channel is out, suspect a broken wire at the tape head before a bad chip.

• Telephone line connected equipment like modems and phones are susceptible to phone like surges. Where a device seems to respond to user commands but does not dial or pickup, suspect a blown part near the phone line connector.

• Sam's Magic Spit(tm). This approach - using a moistened finger to probe LOW VOLTAGE CIRCUITS has come to the rescue many times. Touching various parts of a circuit from the solder side of the board in an attempt to evoke some sort of response can work wonders. Once an suspect area has been identified, use a metal probe or nail to narrow it down to a specific pin.

  The reason this works is that the reduced resistance of your moist skin and your body capacitance will change the signal shape and/or introduce some slight signal of its own.

  • Logic circuits - marginal timing or signal levels will result in a dramatic change in behavior with a slight 'body' load. It has been possible to locate a race condition or glitchy signal on a 305 pin PGA chip using this approach in less time than it would have taken to roll the logic analyzer over to the system under test. Signals which have proper levels and timing are gnerally remarkably immune to this sort of torture.

  • Analog circuits - behavior can again be altered. In the case of audio amps, probing with a finger is just as effective as the use of a signal injector - which is what you are doing - and the equipment is always handy. By evoking hum, buzz, clicks, and pops, locating the live or dead parts of a circuit is rapid and effective.

  • Unknown circuits - where no schematics are available, it may be possible to get the device to do something or locate an area that is sensitive to probing. The function of a section of circuitry can often be identified by observing the effects of touching the components in that area.

    For example, I was able to quickly identify the trigger transistor of in a wireless door bell by using my finger to locate the point that caused the chimes to sound. This quickly confirmed that the problem was in the RF front end or decoder and not the audio circuitry.

  • Bad bypass capacitors - touching the power/signal side of a good bypass cap should result in little or no effect. However, a cap with high ESR and/or reduced uF will not be doing its job bypassing the pickup from your finger to ground - there will be a dramatic effect in audio or video systems.

  Don't get carried away - too much moisture may have unforeseen consequences.

  Depending on the condition of your skin, a tingle may be felt even on low voltage circuits under the right conditions. However, this is pretty safe for most battery operated devices, TTL/CMOS logic, audio equipment (not high power amps), CD players, VCRs (not switching power supply), etc.

  WARNING: Make sure you do this only with LOW VOLTAGE circuitry. You can easily fry yourself if you attempt to troubleshoot your TV, computer monitor, photoflash, or microwave oven in this manner!

On-Line Tech-Tips Databases

A tech-tips database is a collection of problems and solutions accumulated by the organization providing the information or other sources based on actual repair experiences and case histories. Since the identical failures often occur at some point in a large percentage of a given model or product line, checking out a tech-tips database may quickly identify your problem and solution.

In that case, you can greatly simplify your troubleshooting or at least confirm a diagnosis before ordering parts. My only reservation with respect to tech-tips databases in general - this has nothing to do with any one in particular - is that symptoms can sometimes be deceiving and a solution that works in one instance may not apply to your specific problem. Therefore, an understanding of the hows and whys of the equipment along with some good old fashioned testing is highly desirable to minimize the risk of replacing parts that turn out not to be bad.

The other disadvantage - at least from one point of view - is that you do not learn much by just following a procedure developed by others. There is no explanation of how the original diagnosis was determined or what may have caused the failure in the first place. Nor is there likely to be any list of other components that may have been affected by overstress and may fail in the future. Replacing Q701 and C725 may get your equipment going again but this will not help you to repair a different model in the future.

One alternative to tech-tips databases is to search via Google Groups (formerly Deja.com/Dejanews) for postings with keywords matching your model and problem and the newsgroup sci.electronics.repair. See the section: Searching for Information from USENET Newsgroups.

Please see the document: On-Line Tech-Tips Databases for the most up to date compilation of these resources for TVs, VCRs, computer monitors, and other consumer electronic equipment.

Getting Inside Consumer Electronic Equipment

Yes, you will void the warranty, but you knew this already.

Hint: The crowbar and 12 pound hammer are *laset* resorts! Really :-).

Manufacturers seem to take great pride in being very mysterious as to how to open their equipment. Not always, but this is too common to just be a coincidence. Opening the equipment non-destructively may be the most difficult and challenging part of many repairs!

A variety of techniques are used to secure the covers on consumer electronic equipment:

1. Screws. Yes, many still use this somewhat antiquated technique. Sometimes, there are even embossed arrows on the case indicating which screws need to be removed to get at the guts. In addition to obvious screw holes, there may be some that are only accessible when a battery or cassette compartment is opened or a trim panel is popped off.

   These will often be of the Philips variety. (Strictly speaking, many of these are not actual Philips head screws but a slight variation. Nonetheless, a Philips screwdriver of suitable size will work on them.) A precision jeweler's screwdriver set including miniature Philips head drivers is a must for repair of miniature portable devices.

   Sometimes, you will find Torx or a variety of security type fasteners. Suitable driver bits are available. Sometimes, you can improvise using regular tools. In the case of security Torx, the center post can usually be broken off with a pair of needlenose pliers allowing a normal Torx driver to be used. In a pinch, a suitable size hex wrench can substitute for a Torx driver. Places like MCM Electronics carry a variety of security bits.

2. Hidden screws. These will require prying up a plug or peeling off a decorative decal. It will be obvious that you were tinkering - it is virtually impossible to put a decal back in an undetectable way. Sometimes the rubber feet can be pryed out revealing screw holes. For a stick-on label, rubbing your finger over it may permit you to locate a hidden screw hole. Just puncture the label to access the screw as this may be less messy then attempting to peel it off.

3. Snaps. Look around the seam between the two halves. You may (if you are lucky) see points at which gently (or forcibly) pressing with a screwdriver will unlock the covers. Sometimes, just going around the seam with a butter knife will pop the cover at one location which will then reveal the locations of the other snaps.

4. Glue. Or more likely, the plastic is fused together. This is particularly common with AC adapters (wall warts). In this case, I usually carefully go around the seam with a hacksaw blade taking extreme care not to go through and damage internal components. Reassemble with plastic electrical tape.

5. It isn't designed for repair. Don't laugh. I feel we will see more and more of this in our disposable society. Some devices are totally potted in Epoxy and are throwaways. With others, the only way to open them non-destructively is from the inside.

The most annoying (to be polite) situation is when after removing the 18 screws holding the case together (losing 3 of them entirely and mangling the heads on 2 others), removing three subassemblies, and two other circuit boards, you find that the adjustment you wanted was accessible through a hole in the case just by partially peeling back a rubber hand grip! Been there, done that. :(

And on the still lighter side, from an IBM maintenance manual, circa 1925 (displayed in the Chicago Museum of Science & Industry):

"All parts should go together without forcing. You must remember that all the parts you are reassembling were disassembled by you. Therefore, if you can't get them together again, there must be a reason. By all means, do not use a hammer."

When reassembling the equipment make sure to route cables and other wiring such that they will not get pinched or snagged and possibly broken or have their insulation nicked or pierced and that they will not get caught in moving parts. Replace any cable ties that were cut or removed during disassembly and add additional ones of your own if needed. Some electrical tape may sometimes come in handy to provide insulation insurance as well.

For those hard-to-open LCD panels:

(From: Onat Ahmet (onat@turbine.kuee.kyoto-u.ac.jp))

The LCD display housings are usually secured by plastic catches built into the case. They still may have a couple of screws that are positioned in the most innovative places! Obvious places are sides of the display, and under stickers (rub your finger over a sticker and see if you can feel the hole for a screw). Also, try to look around the hinge connecting the LCD to the main housing. Look with the LCD closed, and also open; rotating open the housing might hide some screws from view. Expect it to be awkward! BTW, do not forget small hatches, that do not look like one!

After that, it is patience, and knowing the right place to twist the case to pop it open. Try not to use screwdrivers; they leave unsightly marks along the seam.

Also, if it is your own unit, and you break a few of the catches along the way, do not worry; you can put the housing back together with a few spots of adhesive.

How to Build Obsolescence In Before the Name Goes On

These are in no particular order.

(Portions from various people including Alan Liefting (aliefting@ihug.co.nz), Heath Young (heathryoung@hotmail.com), Craig Osborn (eelcr@worldnet.att.net), Phil Allison (bilup@bigpond.com), Franc Zabkar (franczabkar@dingoblue.net.au), and Sam.)

1. Place metal shields around the power supplies without holes for air circulation. This will ensure power supply capacitors will dry out and make the power supply fail prematurely. And make sure not to use high temperature capacitors. Keeping the electros hot makes the ESR lower so cheaper ones will do.

2. Push as many capacitors as possible into the sides of heatsinks, power transistors, regulators, and power resistors - anything hot!

3. Do not bother with putting thermal conducting paste between heat sink and transistor. It only oozes and dries out anyhow.

4. Do not bother to solder the heavy components or joints subject to thermal cycling. Touch up selected connections by hand? You have to be joking.

5. The following components can be left out during manufacture: protection zener diodes, VDR's, spark gaps, decoupling capacitors, ferrite beads etc. If it works most of the time without them, the expense can't be justified.

6. Keep all factory tests as short as possible. If there isn't a dirt cheap solution to any problems found, don't test for them.

7. Buy the cheapest components from manufacturers who cannot guarantee the longevity of their product. It is easy to have a CRT fail within three years by using impure materials. This will make the cathodes oxide and reduce the emissions giving a dull, hard to read picture. The customer won't realize their TV or monitor has deteriorated but will see newer models with bright vibrant colors and just have to buy one.

8. Fit the so-called head cleaning device to VCR's. This will ensure numerous service calls increasing the customer frustration which will lead them to buy a new product. There is one born every minute.

9. Dispense with EMI/RFI components in the power supplies. As well as producing unacceptable interference, this will also mean that the power supply is more prone to damage from voltage spikes. These problems are by definition the responsibility of the customer anyhow so the result will only be a positive effect on the bottom line.

10. Use the softer plastics rather than the more wear resistant phenolic for kettles and toasters. This will guarantee the consumer will purchase a new product to replace the shabby appliance.

11. Make the covers of heat generating appliances out of painted instead of chrome-plated sheet metal. The paint will darken unevenly with use resulting in an old looking appliance in need or replacement.

12. Do not use spot welding on your heating elements. Spot welding makes a reliable connection. Crimped connections will fail within a short period. This is good (for the manufacturer) since spare parts are not available. The consumer will have to buy a new product and have been conditioned to not expect appliances to be repairable. People like to buy new things anyhow.

13. Install an Appliance Leakage Circuit Interrupter (ALCI) on the cord of the appliance. This is a one time use GFCI (or what I call a GFCK - Ground Fault Circuit Killer). When constructed with suitably cheap parts, it, rather than the appliance will fail but the customer will be informed that they must have gotten the appliance wet.

14. Use the cheaper carbon film resistors instead of the more reliable metal film resistor with better voltage ratings. What the customers can't see won't bother them.

15. Fasten heavy (or just random) parts to the PCB with that white/beige glue that decays after awhile to brown and conductive causing all sorts of nasty problems.

16. Use a design style which will rapidly look dated. This is another ploy in order to have the consumer purchase the latest style regardless of whether the item is working or not. People are slaves to fashion - and they love slaves.

17. Reduce the number of service agencies and the number of products the service agencies will repair for you. This will increase the sale of new products by frustrating the consumers efforts in order to have their item repaired.

18. Fit fast blow fuses inside sealed double insulated appliances that will fail from metal fatigue. (Why did they do this??? - it was sealed with heatshrink onto one of the wires?!)

19. Manufacture equipment as a collection of modules - example. Optics train in certain models of projectors - instead of replacing just a hot mirror ($15 or so) you have to replace the lot! (All optics and LCD screen etc as a module) Now, try getting the poor serviceman to explain why the projector that cost the customer $5,000 costs $3,000 to fix.

20. Encourage consumers to purchase the cheapest items so when someone does make a good product, no one will buy it, and the company will go out of business.

21. Make your spare parts very expensive or do not bother with having spare parts available.

22. When the prototype has been built and working correctly, start removing components until it fails to work properly. Then manufacture it with the minimum parts required to make it work. In mid production run, change selected over designed components to their border line equivalents.

23. If a government regulating agency forces a major recall due to a severe fire hazard, close the current brand name, and start a new brand with a redesigned outside shell that emulates an ergonomic look but with the same internals as before. Add words like "New, Improved, Upgraded, and Leading Edge" to the new marketing slogan.

24. Don't make service manuals or circuit diagrams available. If you do, ensure that only your service agents get one, or price them so highly that the job becomes uneconomical. Think of it this way: Instead of buying the equipment which was the usual way of doing business in the past, the purchase price is now actually only a rental fee for the duration of the warranty. After that, the manufacturer may let the smoke out at any time without notice and thus there is no reason to support repairs. :)

25. Don't identify yourself as the manufacturer. Hide behind your OEM resellers who of course will have no facilities to repair anything except by total replacement.

26. Scrape the numbers off your IC's, or have them stamped with obscure in-house part numbers. You don't want to make repairs too easy for the end user or for a third party repairer who would otherwise be able to source these $1 garden variety parts from any electronics store.

27. Don't stock parts that could reasonably be expected to fail or wear out like battery contacts, flex PCBs, remote control keypads, curly cords. If you must supply them, then do so as part of a complete, uneconomically priced assembly.

28. Use flimsy non-standard (and hence unavailable) connectors for attaching expensive proprietary AC adaptors, chargers, and accessories.

29. Use expensive sealed units which cannot be opened for service without being damaged, and which are powered by an inexpensive internal battery.

30. Have a single solid wire between circuit boards and anything that moves, e.g. sockets at the back of VCRs, or almost any part of a remote control, especially the battery connection. This means that the soldered connection will give up.

31. Have flimsy hinged flaps on a remote control that break after a short time.

32. On a remote control, have rows and rows of identical buttons that have functions that are almost never needed. Also omit functions that would be very handy.

33. Make sure the coax to the tuner of the VCR or TV has no proper mechanical anchorage to the chassis so it takes little more than the house cat to trip on the cable and yank the active innards from the tuner.

34. Make sure all large metal components (particularly the audio in/out sockets at the rear of amplifiers) are only soldered to the same degree as the flimsy IC pins - just soldered sufficiently to pass the production final test.

35. Don't use fiber reinforced plastic gears if you can use plain plastic types.

36. Never use keys to lock shafts to plastic pulleys.

37. Always use etched copper film thin ribbon board interconnects wherever there is maximum flexing such as in laptop screen hinges.

38. Never make rubber drive belts accessible by just removal of the back plate.

39. Use as many non-standard components as possible.

40. Don't use 2 boards if you can mount components on both sides of one board.

41. Always use the smallest possible wattage for a resistor: if the dissipation is 2 watts, then use a 2 watt resistor.

42. Take advantage of exciting new legislation in creative ways to make it illegal for others to make compatible user-replacable parts. No more third party batteries, inkjet cartridges, etc.

43. Add useless complexity to accessories like batteries and inkjet cartridges to make it more difficult for third parties to manufacture replacements. Include warnings about the risks of using third party accessories.

44. Shorten product introduction cycles so that by the time the end-user requires a repair to the item, it's already obsolete.

45. Set the cost of the repair to greatly exceed the cost of a new model of the same type of equipment, which, you just happen (surprise surprise) to have in stock and for sale.

Tools, Test Equipment, and Other Stuff

Hand Tools

Some basic hand tools.

• Screwdrivers of all types and sizes including straight, Philips, Torx. Security bits for some video games, PS2s, etc. Notched straight blade for VCR mechanical tracking adjustment - make or buy.

• Jewelers screwdrivers - both straight and philips. These are generally inexpensive but quality is also quite variable.

• Small socket driver set.

• Hex key wrenches or hex drivers. Miniature metric sizes for VCRs.

• Pliers - long nose, round nose, curved. Both smooth and serrated types are useful.

• Adjustable wrench (small).

• Cutters - diagonal and flush. Linesman's pliers.

• Wire strippers - fixed and adjustable. Crimp tool.

• Alignment tools - (at least a standard RCA type for coils).

• Files - small set of assorted types including flat, round, square, and triangular.

• Dental picks - maybe a reason to go to the dentist? :-) These are useful for poking and prodding in restricted areas (but you knew that).

• Locking clamps - hemostats - for securing small parts while soldering etc.

• Magnetic pickup tool - you can never tell when you will drop something deep inside a VCR. If you keep a strong magnet stuck to your workbench, you can use it to magnetize most steel tools such as screwdrivers. Just keep anything magnetized away from the tape path and magnetic heads.

• Hand drill, electric drill, drill press - one or all. A small benchtop drill press (e.g., 8") is invaluable for many tasks. A good set of high speed bits (not the 1000 bits for $9.95 variety). Also, miniature bits for PCB and small plastic repairs.

• Soldering and desoldering equipment. An entire chapter is devoted to this topic with the name, you guessed it: "Soldering and Desoldering Equipment and Techniques".

Emergency Screw Removal

It may be possible to remove such screws even if nothing in your driver assortment quite fits (short of buying the proper tool, that is - what a concept!). There is also the situation (very common) where someone (we won't say who) has pre-mangled the screw head! Here are a few approaches to try when you are stuck at 2:00 AM on a Sunday morning with an uncooperative screw:

1. Select a driver type (usually Philips) and size that privides the best grip. Then apply as much pressure as is safely possible without destroying anything and attempt to turn the screw. What you want to avoid is slippage - once the blade slips, the head will be quickly destroyed and then you are left with options (2) or (3), below. For a jeweler's type screwdriver, clamping something larger to its shaft can provide valuable additional leverage.

2. Use a hand grinder (e.g., Dremel tool) or thin file to create a slot in the screw head which one of your straight-blade screwdrivers will fit. Obviously, take care to avoid damage to adjacent parts and dam off the area to prevent grinding chips from getting over everything.

3. Grab the center and edge of the screw with a pair of sharp diagonal cutters and turn it. This, of course, also damages the screw head and if you are too forceful, will break your cutters as well.

4. Drill out the screw using a bit just large enough to sever the head from the shank of the screw. Then, use a pair of needlenose pliers to unscrew what remains. For large screws, drill only part way and then use a screw extractor like Easy-Out(tm).

5. Superglue the screwdriver or some other suitable tool to what's left of the screw. Wait till it hardens and turn.

6. There are also products available for the purpose of improving the grip of screwdrivers. For example: ScrewGrab.

7. For screws into plastic holding metal covers, remove all other screws so the cover can be used to pull on the screw and heat the screw with a soldering iron. With care, it will melt its way out but the plastic will solidify to a smaller hole that can be used to install a new screw. Where the cover is also plastic, it may melt first so probably not a good idea.

Note: some of these screws have had some material like Lock-Tight(tm) (which looks like colored nail polish) applied to the top to prevent the screw from loosening on its own. This also prevents the blade of a screwdriver from properly seating, so removal is essential before attempting removal.

Plastic Screw Thread Repair

1. Install a larger screw in original worn hole. :) For repairs where the appearance isn't important, this may be the best solution.

2. Use a soldering iron from the hidden side to "adjust" the hole. Doing this with the screw in place will result in proper threads being preformed.

3. Fill the hole with a mixture of the same type of powdered plastic and solvent or other similar material. When dry, drill a pilot hole and then install the original screw.

4. Glue a metal nut to the underside of plastic and use a machine screw.

There are many other possibilities.

To avoid this problem in the future, realize that plastic is very soft and it is essential to gently start the screw into the hole to get a feel for it properly mating with the existing threads. The use of an undersized screwdriver to get the screw started may be helpful in that it won't accidentally apply too much torque and strip the threads. Something that is less obvious is that screws for plastic are often made with a wide thread and a narrow thread wound that alternate, sort of like a deformed hunk of DNA. :) With these, there is only one proper way for them to mate with an existing hole and forcing them is asking for stripped threads and a fine strand of plastic being pulled out along with the loose screw.

About Those Other Funny-Headed Screws

As well as Phillips, there are Pozidriv and JIS:

Pozidriv screws can be recognized by the 'starburst' - the little lines on the head between the main slots. These are very common (certainly in Europe) in all sorts of equipment.

• There are also JIS (Japanese Industry Standard) heads. These _look_ just like Philips, but the screwdriver is a little flatter on the end. Not surprisingly these do turn up in Japanese stuff.

It's not uncommon for all 3 to be used in the same equipment, especially if subassemblies were made by different companies.

(From: Robert McPherson (rm502@bellsouth.net).)

There is a type of screwdriver called a "Reed & Prince" which fits these screws which are similar in appearance to Phillips screws. Cooper tools makes them.

Workbench and AC Power

A size of 3 x 6 feet should be adequate, longer is better if you have the space. Workbench height is typically 36 inches. Make sure the legs are sturdy and rigid - some equipment can be quite heavy. Get yourself a comfortable stool to sit on for those marathon troubleshooting sessions.

The surface can be laminate, particle board, plywood, butcher block, or some other insulator. It shouldn't have a dramatic pattern though since small parts will be hard to find. Wood products should have multiple coats of varnish or polyurethane. Using a cheap material that can be replaced will enable the surface to be rejuvenated after it gets pitted and burnt - as it invariably will after awhile. An antistatic surface is desirable but probably expensive to put on the entire workbench so just get an antistatic matt for use when needed. (An antistatic surface isn't quite a perfect insulator but has just enough conductivity to minimize the buildup of static electricity, essential for any work with devices like CMOS ICs and laser diodes that can be destroyed by even a small static discharge.)

Install a shelf or shelves along the back that are about half the depth of the workbench surface to hold smaller pieces of test equipment, power supplies, parts cabinets, and other odds and ends. Add a shelf or shelves underneath for storage.

Install AC outlets along the rear edge, vertically so debris can't fall into the holes. How many? The more the merrier - they will all get filled no matter how many are there! At a minimum, one every 6 inches or a duplex every foot, double this won't hurt. Power the workbench from two branch circuits fed from opposite sides of the 115-0-115 VAC (in the U.S.A.) Consider including at least one 230 VAC outlet (in the U.S.A.). Providing some outlets that are switched with power indicator lamps and protected by fuses or circuit breakers. Most outlets, particularly those used to plug in equipment being worked on, should be GFCI (Ground Fault Circuit Interrupter) protected for safety. But a few - clearly marked "NOT GFCI PROTECTED" - should be available for equipment that will not function reliably on a GFCI with the understanding that these lack such protection. Most test equipment and power supplies with properly wired grounded power cords do not need to be GFCI protected but won't complain if they are. However, some equipment may nuisance trip (immediately or at random) GFCIs even if functioning properly.

The total cost can be well under $100 for all of this even if the materials and parts are purchased new. With some reasonable scrounging abilities, it can be a lot less.

Basic Test Equipment

• DMM and/or VOM. I prefer to have both. A good old Simpson 260 is better in many ways than a cheap digital multimeter. For most measurements, I still use a 25 year old Lafayette (remember them?) VOM. I only go for the DMM when I need to measure really low ohms or where better accuracy is needed (though this can be deceptive - just because a DMM has 3-1/2 digits does not mean it is that accurate - check you manual, it may prove enlightening). The Simpson 260 also has a nice 5000 V AC/DC scale which the others lack.

  A fancy expensive multimeter is not needed, at least not while you are just starting out (and likely to make some occasional mistakes like attempting to measure line voltage on the ohms scale.) However, if someone offers to give you a nice Fluke DMM, don't turn it down :-).

  Scales for transistor, capacitor, frequency counter, etc. are not really essential. A diode test function on a DMM is needed, however, to properly bias semiconductor junctions. Even this is not useful for in-circuit tests or for some power transistors or transistors with built in damper diodes and/or base resistors.

  Make sure you have a good well insulated set of test probes. This is for your own safety as you may be measuring relatively high voltages. Periodically inspect for damage and repair or replace as needed. If the ones that came with your multimeter are substandard - flimsy connectors or very thin insulation, replace them as well.

  A high impedance high voltage probe is sometimes useful for TVs and monitors. You can build one of these which will suffice for most consumer electronics work.

• AC clamp-on ammeter. This permits the measurement of currents in appliances or electrical wiring without having to cut any wires. At most, you will need an easily constructed adapter to permit access to a single conductor of a line cord. This may be an option for your multimeter.

• Oscilloscope - dual trace, 10 to 20 MHz minimum vertical bandwidth, delayed sweep desirable but not essential. A good set of proper 10x/1x probes. High vertical bandwidth is desirable but most consumer electronics work can be done with a 10 MHz scope. If you get into digital debugging, that is another story - 100 MHz and up will be required. If money is no object, get a good digital storage scope. You can even get relatively inexpensive scope cards for PCs, but unless you are into PC controlled instrumentation, a stand-alone scope is much more useful.

  I would recommend a good used Tektronix (Tek) or Hewlett Packard (HP) scope over a new scope of almost any other brand. You will usually get more scope for your money and these things last almost forever. Until recently, my 'good' scope was the militarized version (AN/USM-281A) of the HP180 lab scope. It has a dual channel 50 MHz vertical plugin and a delayed sweep horizontal plugin. I have seen these going for under $300 from surplus outfits. For a little more money, you can get a Tek 465 or 465B (slightly newer but mostly similar specifications) 100 Mhz scope ($200 to 600) which is what I use now. The HP-180 is still fine but I couldn't pass up a really good deal. :) The Tek 465/B or other similar model will suffice for all but the most demanding (read: RF or high speed digital) repairs. (See the additional comments below on the Tek 465 as well.) From my experience with this scope many years ago and now as well, I really do agree with some who say that this is the best scope Tektronix ever designed.

  Auctions like eBay can sometimes be a source of good used Tek and other scopes at reasonable prices though sometimes the bid price goes way beyond what is reasonable. :) A search for "oscilloscope" will typically turn up several hundred hits. However, to have any confidence in the operational condition of a scope, the seller must be reputable and know something about testing them. A warranty may be of limited value since a major part of the cost of a used scope is likely to be the shipping and you'd end up having to pay that both ways. Check out Phil's Tek Scope Prices on eBay List as well as catalog pages of surplus test equipment dealers. A Web search (e.g., Google) will usually turn up enough sites for any specific model to provide both specifications and typical prices from surplus equipment dealers (which are usually high!).

  My instant checklist for a used scope:

  • Bright, sharp trace, no screen burns, short warmup time.
  • Vertical amp(s) operational on all ranges.
  • Horizontal timebase(s) operational on all ranges.
  • Stable triggering at low and high end of frequency range.
  • Switches and controls reasonably noise-free (may need cleaning though).
  • Decent cosmetic condition, all knobs and buttons present, no signs of major trauma.

  You don't absolutely need an oscilloscope when you are just starting out in electronics but it would help a great deal. It need not be a fancy one at first especially if you are not sure if electronics is for you. However, being able to see what is going on can make all the difference in your early understanding of much of what is being discussed in the textbooks and the newsgroups. You can probably find something used that will get you through a couple of years for less than $100. An oldie but goodie is much better than nothing at all even if it isn't dual channel or high bandwidth!

  And a note about digital versus analog scopes: Analog scopes are what we used to think of as an oscilloscope: The CRT is the place where the waveform is generated. Digital scopes use a fast A/D converter to capture data in memory in the form of 1s and 0s and then display this on a raster-scan CRT (like a computer monitor screen). Digital scopes are automatically storage scopes and are great for analyzing waveforms. However, most older digital scopes are really poor at real time display and in addition, appear to have been designed by computer programmers, not test equipment engineers. Ever try to play a menu-driven piano? :) For general electronics and troubleshooting, I'd rather have a 20 year old Tek analog scope than a 5 year old digital scope costing 25 times as much. The inherent real-time presentation of an analog scope can be invaluable when attempting to observe the subtle characteristics of a waveform. Those who go through school never having touched a true analog scope have missed out on a great experience.

• Logic probe - for quick checks of digital circuitry for activity. A logic pulsar can be used to force a momentary 1 or 0. Some people swear by these. I consider them of marginal value at best.

• TV set (color is desirable) and/or video monitor for testing of video equipment like VCRs, camcorders, laserdisc players, etc. I have an old CGA monitor which includes an NTSC input as well.

  A great deal of information can be gathered more quickly by examining the picture on a TV or monitor than can be learned from the video waveform on displayed on a scope.

• VCR or other video signal source for testing of video monitors and TVs. These will have both RF (F connector) and baseband (RCA jacks) outputs.

• Stereo tuner or other audio signal source for testing of audio equipment.

• Audio signal generator. A function generator (sine, square, triangle) is nice as well. The usual audio generator will output from a few Hz to about 1 MHz.

• Audio amp connected to a loudspeaker. The input should be selectable between line level and mic level and be brought out through a shielded cable to a test probe and ground clip. This is useful for tracing an audio circuit to determine where a signal is getting lost.

• Signal injector. A readily accessible portable source of a test tone or other signal (depending on application) that can be introduced into the intermediate or early stages of a multistage electronic system.

  For audio, a simple transistor or 555 timer based battery powered oscillator can be built into a hand held probe. Similar (but generally more specialized) devices can be constructed for RF or video testing.

• RF signal generator. For serious debugging of radio and tuner front-ends. These can get quite sophisticated (and expensive) with various modulation/sweep functions. For most work, such extravagance is unnecessary.

• LCR meter - a capacitor tester is desirable but I prefer to substitute a known good capacitor rather than trusting a meter which will not test under the same conditions as exist in-circuit.

• Adjustable power supplies. At least one of these should bo of the totally indestructable variety - one you can accidentally short out without fear of damage. Mine is a simple 1 amp 0-40 V transformer and rectifier/filter cap affair with a little Variac for adjustment.

• The following book has a number of simple test equipment projects you can build with readily available parts:
  • Test Equipment Projects You Can Build
    Delton T. Horn
    Tab Books, a division of McGraw-Hill, Inc., 1992
    Blue Ridge Summit, PA 17214
    ISBN 0-8306-4154-8 (hardcover), 0-8306-4155-6 (paperback)
    

Jerry's Comments on Used Scopes and the Tek 465

If you are buying a used 465, look for the 465B. It is a better unit, and is the same price most of the time. Take care that this scope is about 20 years old, and there is no support from Tek on it. The replacement parts are not available if something blows. I used to have a few of them. One needed a CRT, and the other I sold while it was still working. For consumer electronics, you will get by with a 100 MHz unit, but it is preferable to have over 200 MHz bandwidth if you want to do front end service on consumer FM radio receivers. Read up on Nyquist and you will see the answer.

If you also call Tektronix technical services, tell them that you are looking for a used Tek scope to be used for hobby purposes. They will be very helpful in giving you any information you require. They will even recommend models and what to look for. If you talk to their sales people, they will sometimes even give you their authorized dealers who handle used Tek equipment so that you can shop around.

If you go a bit more for your used scope you can get a 200 or 300 MHz unit that is a newer version of an analog scope. It will have improvements over the 465 series. Look at the 2000 analog series scopes. These have a lot of enhancements like on the screen display. This will be very handy for precise work. When buying any type of scope, I would stress that the Tektronix is the best. If you find a good working used one, you will have a very high quality product, and it should give you years of service. Most of the analog scope that they made include the TV sync options.

Even if you buy a used one, and the parts are not available, it pays then to buy a second used one and you will have spare parts. These scopes used to cost in the many thousands of dollars when new, and you are probably paying between eight hundred to fifteen hundred for a used one (somewhat cheaper now, even from surplus companies. --- Sam). These scopes will be far superior to even the newer ones from the consumer level scopes. In 1978 I believe my company paid over $8,000 for the 465B scope new. A new Chevy fully loaded was less!

Repairing Tectronix 400 Series Scopes

The most likely causes of a totally dead scope, or one with multiple system problems, are shorted tantalum "dipped" capacitors dragging down one or more power supply rails. Apparently, Tek used a batch of unreliable caps on the some of the 400 Series scopes. While aluminum electrolytics usually just dry out with decreased capacitance and increased ESR, these dipped tantalums go short circuit. Fortunately, the design of the switching power supplies in these scopes is such that the controller shuts down from a serious overload or short rather than letting its smoke out. If the overload is on only one voltage rail and not severe (e.g., through a resistor), only that voltage may be low or absent resulting in loss of functionality or the supply may cycle on and off, but not a totally dead scope.

So, the first step is (WITH POWER OFF) to check the resistance of each voltage test point to ground with a multimeter. While the expected resistances may not be known except from a service manual (if that), anything very low (e.g., 10 ohms) is suspect. Here are typical values measured on a Tek 485 using a Fluke 87 DMM with the black lead on ground: +50 V, 2.1K ohms; +15 V, 89 ohms; +5 V, 70 ohms; -5 V, 222 ohms; -15 V, 152 ohms. The resistance for +5 V changes significantly depending on front panel settings and which incandescent indicator lamps should be lit and may go below 35 ohms. On this scope, the -15 V rail originally measured about 10 ohms due to a bad cap. Where one of these is found, attempt to determine the location of the short to a specific circuit board. Then, trace the wiring on that board to locate the possible bad caps. A good DMM or milliohmmeter can help to track down the cap since PCB foil resistance is high enough to be measured and the resistance to ground will be lowest at the location at the bad cap. At this point, unsoldering one lead of each cap and checking its resistance is the safest approach. With care, this can be done from the component side of the board which is fortunate since removing some of these large PCBs can be a royal pain. Heat the lead with a soldering iron and pull it free. Then, use a vacuum desoldering tool ("SoldaPullet") to clear the hole. Check the resistance of the cap and/or across the supply rail to determine if you found the correct one. The bad cap mentioned above was found in about 5 minutes in this manner. There are typically only a few of these caps on each board but it's possible for the bad one to be on a board that isn't easily accessible. It may be even easier as sometimes the bad cap will have split open and thus be obviously bad. I've also heard of cases where the cap exploded and the only thing left were its legs! (The scope may even have worked fine at that point with the short removed!)

However, any low value resistors between the power supply rail and shorted cap may become quite toasty, burnt, and carbonized, also resulting in a very noticeable stink. :) And the carbon may even short to a PCB via if there is one underneath it. :( :) I had this happen on the same Tek-485 a few years later, where it also took out a 2N2222 transistor nearby. But even though the resistor's surface was burnt to crispy carbon, when cleaned off, the resistance was still correct. (However, I did replace it.)

Where these approaches don't work, or for the lazy but daring among us, the alternative is to apply voltage from an external adjustable current limited supply to the bad power rail. If the bad part isn't a perfect short circuit, it will dissipate heat and let its smoke out or explode (or a one of those series resistors may do so instead). Wear safety glasses! If this doesn't happen, it may actually be possible to power up the scope with the external voltage applied to determine functionality. In either case, I won't be responsible for any destroyed equipment should this be done.

So You Can't Afford a $20,000 Transient Event Recorder?

However, there may be no need for such extravagance. If you have an oscilloscope and camcorder or video camera/VCR, you probably have all that is needed.

For a TV or monitor, point the camera at the CRT and the scope screen so that they are both in the picture and record on a 6 hour tape. Then, when your event takes place, you have a permanent record!

That old video camera will be perfectly adequate. It doesn't need a 100X digitally stabilized enhanced reprocessed zoom or 1/10,000th second shutter. It doesn't even need to be color!

Sure, this won't capture the 1 ns glitch. But, for the occasional flash in the picture, it is more than adequate to eliminate a video signal line as the source of the problem.

Extensions to more convoluted problems are left as an exercise for the student!

Transformers - Isolation and Variable

Isolation Transformers

Since Earth Ground and the Neutral of the power line are connected together at your service panel (fuse or circuit breaker box), grounds like cold water pipes, test equipment chassis, and even a damp concrete floor make suitable returns for the line voltage (Hot or live wire). Since this is just as true with the conductor being being a wire or your body, such a situation is very dangerous.

An isolation transformer as its name implies provides a barrier such that accidental contact with an earth ground results in negligible current flow (only due to the parasitic capacitance and inductance of the transformer) - a slight tingle at worst. This also protects your test equipment as well as the device you are troubleshooting since a similar accidental contact can result in a short circuit, sparks, smoke, and many destroyed parts.

The schematic for a typical isolation transformer is shown below:

                               _        1:1
                H o-----/ ----- _------+    +-----------o 115 V
                       Power  Fuse      )||(
                       Switch           )|| +-----------o 105 V
                                        )||(
                                        )||(
                                Primary )||( Secondary
            Tied together at            )||(
            service panel               )||(
            |                           )||(
            |                           )||(
            +-> N o----------+---------+ |  +---+--------o Return
            |                |  4.7 M*   |      |
            |                +---/\/\----|------+
            |                            |
            +-> G o----------------------+--------------o Ground

Note: Ground is included on the secondary side. This is actually needed for safety with certain types of equipment like microwave ovens where the HV return is to the chassis. Most other consumer electronic equipment and appliances will only have a 2 wire cord and thus not use the Ground. However, a potential safety hazard can arise if some other piece of equipment develops a ground fault resulting in a live, non-isolated part being user-accessible so this must be taken into consideration in deciding whether to ground the secondary side.

Where your outlets are only 2-prong without safety Ground, an isolation transformer will still provide most of the benefits, and if the equipment being tested has a 2-prong plug - as with most consumer electronics - it is irrelevant anyhow except for the grounding of the transformer itself.

The resistor (*) is desirable to permit any static charge to leak off to ground. Since it is quite large - 2 M ohms - no perceptible current will flow between the secondary and primary sides but this value is low enough to dissipate any static charge. CAUTION: The resistor must be a high voltage rated type (as in 4,200 V isolation, large size light blue color to assure that arc over will not result due to voltage differences that may be present when the isolation transformer is being used in its normal manner.

Although the power line Neutral and Ground wires are tied together at the main service panel (fuse or circuit breaker box), the transformer prevents any significant current flow between any of its outputs and earth ground should a fault occur.

Even if you were standing with bare feet in a puddle of salt water on a concrete floor (noting that this is definitely NOT recommended) and were to touch something connected to the secondary of the isolation transformer or its return, or equipment circuitry attached to these, there is no direct return path for current to flow through you.

However, this shouldn't encourage a false sense of security. If you were to touch two points at different potentials on the secondary side, you could still be fried! And some equipment like microwave ovens use their chassis, and thus ground, as the high voltage return so an isolation transformer is of limited value for these whether it passes ground through or not.

Isolation transformers can be purchased or constructed from a pair of similar power transformers connected back-to-back. I built mine from a couple of old tube-type TV power transformers mounted on a board with an outlet box including a fuse. Their high voltage secondary windings were connected together. The unused low voltage secondary windings can be put in series with the primary or output windings to adjust voltage. See the section: Typical Homemade Isolation Transformer.

For super critical applications like in hospitals where every microamp of leakage counts, special isolation transformers are available (no doubt at equally super cost) which have shielding between the primary and secondary to minimize the inter-winding capacitance and inductance as well. This should not really be necessary for general servicing.

Note: Not all definitions of the term 'isolation transformer' are created equal! For some purposes, this may mean just preventing line born electrical noise from passing to the equipment. So, if you acquire something called an 'isolation transformer' on its nameplate, confirm that the primary and secondary are indeed not tied together by a low resistance. If they are, it can probably be modified for service needs by disconnecting a jumper but it may not have the insulation ratings desirable for high voltage isolation.

(From: Filip "I'll buy a vowel" Gieszczykiewicz (filipg@repairfaq.org).)

Ever wonder how those guys repair HV transformers running 200 kV without shutting off the power lines feeding the city? They use *very well isolated* cherry pickers! The guy on that platform is working on ONE wire which - since he's not connected to the ground - is at ZERO potential! That wire has no reference at all so no current flows. And he prays each morning that it stays that way or he goes off with a flash! [ugh!].

You're doing something like that on a much safer level. :)

Typical Homemade Isolation Transformer

                                       +-------------------------o 109 V
                                       |
                                       |     +-------------------o 121 V
                                       |     |
                                       | +---------------+
                                       | |   |           |
                          || +--o NC   | |   +---+ ||    |
                          ||(          | |        )||    |
                          ||(          | |  6.3 V )||    |
                          || +--o NC   | +-------+ ||    |
                   _      ||(          |          )||    |
       H o--/ ----- _---+ ||(          |    6.3 V )|| +--+-------o 115 V
           Power  Fuse   )|| +--o NC   +---------+ ||(
           Switch        )|| +-------------------+ ||(
                   115 V )||(                     )||( 115 V
                         )||(                     )||(
                         )||( 350 V         350 V )||(
       N o---------+----+ ||(                     )|| +----+-------o Return
                   |      || +--o NC       NC o--+ ||      |
                   |      ||(                     )||      |
                   |      ||(                     )||      |
                   |      ||( 350 V         350 V )||      |
                   |      ||(                     )||      |
                   |      |  +-------------------+  |      |
                   | Pri1 |  Sec1              Sec2 | Pri2 |
       G o----------------+-------------------------+-------------o Ground
                   | Transformer 1    2M*    Transformer 2 |
                   +------------------/\/\-----------------+

Note that there should be a fuse in the primary to protect against faults in the transformer as well as the load. A slow blow type should be used in the primary circuit. The inrush current of the transformer will depend on the part of the cycle when the switch is closed (worst is actually near the zero crossing) as well as the secondary load. To protect the load, a fast blow type in the secondary is recommended. However, the inrush current of the degauss coils in TV sets and monitors, for example, will often pop a normal or fast blow fuse when no actual problems exist. (It is probably a good idea to disconnect the degauss coils while testing unless they are suspected of being the source of the problem.)

The 2 M resistor (*) is to bleed away any static charge as described above.

The power/VA ratings of the transformers you use need to be greater than your expected load. And, since some equipment like TVs and computer monitors draw a lot of current at power-on (from the degauss circuit), the isolation transformer will limit the peak current and may cause problems during startup (though overall, the limited current may prevent some types of disasters!). In any case, don't expect a pair of 6.3 VAC, 1 A transformers wired back-to-back to be useful for testing much of anything!

Where your outlets only have 2 prongs (without safety Ground), leave out the G->Ground connection and DON'T tie the transformer cases/frames together. If the equipment being tested has a 2-prong plug, it's irrelevant anyhow except for the grounding of the transformer itself. With two separate transformers, there would have to be a fault in both to result in a safety hazard - a very low probability event.

Also see the section: Isolation Transformers from Dead Microwave Ovens.

(From: David Moisan (dmoisan@shore.net).)

It's not as hard as you think to find inexpensive isolation transformers. At the next hamfest, look for someone selling dead UPS's (Uninterruptible Power Sources) or other power conditioning equipment. Isolation transformers are often sold for use in the computer industry; that's how I got mine. 250 VA for $20, and I could have gotten 1000 VA for $50 if I wanted. Definitely increases my safety *and* confidence level!

Isolation Transformers from Dead Microwave Ovens

However, note that microwave oven transformers are usually designed with as little copper as possible in the primary winding and do go into core saturation at normal line voltage with no load. For example, measurements using a clamp-on AC ammeter of a transformer from a mid-size microwave oven shows:

            Input VAC   Input Amps
           ------------------------
                80           .3
                90           .6
               100          1.1
               110          2.0
               115          3.0
               120         >4.0

Thus, this sort of approach isn't recommended unless you really need the high capacity - testing of other microwave ovens or ion laser power supplies, for example!

A pair of these trnasformers can be connected in a similar manner to the tube-type TV power transformers described in the section: Typical Homemade Isolation Transformer, there are a few more things to keep in mind:

• These transformers are DANGEROUS. Their high voltage output is between 1,500 and 3,000 VRMS at AMPS - an instantly deadly combination. Therefore, thoroughly insulate the connections between the HV secondaries.

• The high voltage returns are connected to the cores so these must be tied together AND to earth ground for safety.

• These transformers may not be rated for continuous duty operation. So, they should probably not be left plugged in when not in use.

• The more limited capacity of a small isolation transformer can sometimes protect you from yourself - preventing the burnout of a horizontal output transistor due to excessive load or carelessness. You will have no such guardian looking over your shoulder with a microwave oven monster!

How Safe is a Homemade Isolation Transformer?

Keep in mind that I am not talking about using something that has been rusting away in a damp basement for 20 years. The power transformers from tube-type TVs or audio amplifiers must have been designed with isolation requirements in mind to obtain regulatory approval in the first place since they are used in equipment where the user may come in contact with metal parts.

Also, the use of an isolation transformer is no excuse to ignore the other aspects of safe troubleshooting.

It is easy to test for AC and DC leakage - and this should be done - to be sure that your transformers are in good condition. With two transformers, the probability of a failure is even smaller - 1/(P*P). Personally, I would trust the homemade transformer over a cheap import any day!

Variable Autotransformers

The internal wiring of a typical Variac is shown below:

                 _                1 
          H o---- _-----/ ------>o--+     Tap 1: 0 to 115 VAC
               Fuse 1  Power      2  )||
              (Input)  Switch    o--+ ||  Tap 2: 0 to 140 VAC
                                     )||
                                     )||      _
      Tied together at               )<------- _--------o Adjustable output
      service panel           Power  )||     Fuse 2
      |              220       LED   )||    (Output)
      |          +--/\/\--|>|--|>|--+ ||
      |          |                   )||
      +-> N o----+------------------+-|-----------------o Return
      |                               |
      +-> G o-------------------------+-----------------o Ground

CAUTION: Keep any large transformer of this type well away from your monitor or TV. The magnetic field it produces may cause the picture to wiggle or the colors to become messed up - and you to think there is an additional problem!

Note: the 'Power LED' circuit is soldered directly to a winding location determined to produce about 6 VAC.

• Sam's Rule #61453: Your lab or shop can never have too many Variacs!
• Sam's Rule #61454: If you only have a single Variac, it should be LARGE!

Wiring a Variable Autotransformer

Wiring is straightforward if you have acquired a bare unit (the following assumes a 115 VAC line, the extension to 230 VAC should be obvious):

• Decide on the output voltage range and direction of rotation (clockwise should always be used to increase output as far as the user is concerned but depending on mounting, actual direction of the shaft with respect to the body of the unit may be either way):
  • For 0 to 115 VAC output, Hot and Neutral go between the ends of the winding with Neutral at the terminal where the wiper will be when you want the output to be 0 VAC; The output goes between Neutral and the wiper.

  • For 0 to 140 VAC output, Hot is moved to the tap about 20 percent away from the terminal where the wiper will be when the output is at 140 VAC; The output goes between Neutral and the wiper as above.

  • For some (mostly small) Variacs that do not have intermediate taps, it may still be possible to add a tap to permit 140 VAC operation. However, this will reduce the number of turns on the primary and could lead to overheating from core saturation if the design is marginal. Most of these are overdesigned and this shouldn't be an issue. But, nonetheless, if you try this, monitor the temperature of the unloaded Variac for, say, an hour to make sure it doesn't get excessively hot.

• Include a primary-side power switch and power-on indicator lamp. In the old days, a neon lamp would be used (e.g., NE2H with a 47K ohm resistor). Nowadays, neon lamps may be hard to find. An alternative as suggested above is to add a tap on the Variac winding at about 6 to 10 VAC and use an LED and current limiting resistor.

• Provide fuses for both input and output. They should be the same rating as the Variac. The fuse for the input protects against primary side shorts. The one for the output protects the Variac winding from excessive load. Commercial units may only have one fuse but fuses are inexpensive and the added protection won't hurt.

• Use an adequately rated grounded cordset and mount everything in a well insulated box. The Variac frame and box (if made of metal) should be grounded.

Variable Isolation Transformers

Variac/Isolation Transformer with Current Limiting

Constant Voltage Ferrorsonant Transformer

Note that while isolation may be provided, it is NOT inherent in this technology. Some types may use autotransformers and thus have no isolation.

(From: Dave Martindale (davem@cs.ubc.ca).)

The simplest version has fairly ordinary-looking primary and secondary windings wound on the centre leg of a shell-type transformer core. Unlike a normal transformer, where the primary is wound over the secondary (or vise versa), the primary and secondary windings are physically separated. Magnetic shunts (chunks of transformer steel) are inserted between the centre and outside legs of the core at a point between the primary and secondary winding. These magnetic shunts provide a flux path around the primary that bypasses the secondary winding, producing lots of leakage inductance. This is what limits the current when the secondary is shorted.

Meanwhile, the secondary winding is in parallel with a capacitor, chosen to make the secondary resonant at 60 Hz. The resonance drives the portion of the core inside the secondary winding into saturation, which limits the amplitude of the secondary voltage. Changes in primary voltage have almost no effect on secondary voltage over the regulating range.

Now, the above is actually a simplification. In real CV transformers, the secondary actually has enough turns to step up the voltage by a factor of several, so the capacitor is operating at several times line voltage. This allows the capacitor to be lower capacitance for resonance, which is physically smaller and cheaper than what you'd need at 115 V. The actual output voltage is obtained from a tap on the secondary where the voltage is 115 V or so.

Also, the transformer I've described so far outputs a pretty square waveform. That's great for the input stage of a DC power supply, but not for some AC loads. The commercial CV transformers I see use a "harmonic neutralized" design that gives an output closer to a sine wave. Instead of one secondary winding, there are two, with another pair of magnetic shunts between the two secondaries. The capacitor is connected across the two secondary windings in series. The output voltage is taken from just the "middle" secondary winding. In the Sola transformer, there's also an air gap in the centre leg of the core, at the end where the 3rd winding is. I don't understand how the extra winding and shunt cancel some of the 3rd harmonic output, but they do.

The Series Light Bulb Trick

Actually using a series load - a light bulb is just a readily available cheap load - is better than a Variac (well both might be better still) since it will limit current to (hopefully) non-destructive levels.

What you want to do is limit current to the critical parts - usually the horizontal output transistor (HOT). Most of the time you will get away with putting it in series with the AC line. However, sometimes, putting a light bulb directly in the B+ circuit will be needed to provide adequate protection. In that location, it will limit the current to the HOT from the main filter capacitors of line connected power supplies. This may also be required with some switchmode power supplies as they can still supply bursts of full (or excessive) current even if there is a light bulb in series with the AC line.

Actually, an actual power resistor is probably better as its resistance is constant as opposed to a light bulb which will vary by 1:10 from cold to hot. The light bulb, however, provides a nice visual indication of the current drawn by the circuit under test. For example:

• Full brightness: Short circuit or extremely heavy load - a fault probably is still present.

• Initially bright but then settles at reduced brightness: Filter capacitors charge, then lower current to rest of circuit. This is what is expected when the equipment is operating normally. There could still be a problem with the power circuits but it will probably not result in an immediate catastrophic failure.

• Pulsating: power supply is trying to come up but shutting down due to overcurrent or overvoltage condition. This could be due to a continuing fault or the light bulb may be too small for the equipment.

The following are suggested starting wattages:

• 40 W bulb for VCR or laptop computer switching power supplies.
• 100 W bulb for small (i.e., B/W or 13 inch color) TVs.
• 150-200 W bulb for large color or projection TVs.

Depending on the power rating of the equipment, these wattages may need to be increased. However, start low. If the bulb lights at full brightness, you know there is still a major fault. If it flickers or the TV (or other device) does not quite come fully up, then it should be safe to go to a larger bulb. Resist the temptation to immediately remove the series light bulb totally from the circuit at this point - I have been screwed by doing this. Try a larger one first. The behavior should improve. If it does not, there is still a fault present.

Note that some TVs and monitors simply will not power up at all with any kind of series load - at least not with one small enough (in terms of wattage) to provide any real protection. The microcontroller apparently senses the drop in voltage and shuts the unit down or continuously cycles power. Fortunately, these seem to be the exceptions.

Combination Variable Isolation Transformer and Series Light Bulb Unit

• A Variac and isolation transformer or variable isolation transformer. Include a power switch and BIG RED power-on indicator as well as primary and secondary fuses or circuit breakers.

• A series light bulb bank consisting of 25, 50, 100, and 200 W light bulbs in parallel with individual switches for each. By selecting an appropriate combination of switch positions, any wattage from 25 to 375 W can be set up in 25 W increments. An additional switch in parallel with the light bulbs can be used to bypass them entirely. The light bulbs should be outside any enclosure so (1) they are clearly visible and (2) their heat won't cook the components inside the case!

• AC voltmeters on the isolation transformer output and final output; AC ammeter in series with the load.

Using a Light Dimmer or Similar Device as a Variac?

The behavior of a phase control device like a light dimmer depends critically on what sort of load it sees. If the dimmer sees mostly a resistive load, it will work reasonably well and survive. However, most electronic equipment doesn't fall into this category. If the dimmer is attempting to drive a piece of equipment with a lot of capacitance or inductance, at the very least it will behave strangely with the control range squashed to one end or the other, or the output voltage will change suddenly rather than smoothly. But more likely, it will self destruct and/or damage the equipment due to the strange waveform, which may result in a peak output voltage that approaches full line voltage even at relatively low settings. There's also usually a minimum load below which it won't do anything predictable. In short, get a proper Variac. You know my motto: "You can never have too many Variacs!". :) Surplus Variacs are readily available including on eBay.

What About the Scope Ground?

In general, oscilloscopes SHOULD be earth grounded. The only time this is not the case is if you are attempting to measure signals in a line-connected device like many TVs and switching power supplies, and are not using an isolation transformer. However, this is a very dangerous setup and should be avoided if at all possible. With line-connected equipment, the return or ground reference is not at earth ground potential due to the bridge rectifier or voltage doubler often used in the power supply front-end.

Without an isolation transformer, connecting the scope ground clip to the return will result in a short through the ground lead between the equipment and earth ground. There will be smoke and possibly blown components as well in the equipment being tested, and possibly in the scope as well. The key here is that neither output of a bridge rectifier (the most likely front end configuration in line-connected power supplies) is at Earth Ground potential. They both have a large AC component with respect to Earth ground. Consider:

                     D1
        H o-----+----|>|-------+---------+-----o DC+
               ~|    D2        |+        |
      In from   +----|<|----+  |       +_|_
      AC line        D3     |  |      C ___
                +----|>|----|--+       - |
                |    D4     |            |
 ---+-o N o-----+----|<|----+------------+-----o DC-
    |          ~   Bridge       -
    +-o G o------------------------o Earth Ground (also connected to scope)
   _|_
  ///

Hot (H) and Neutral (N) are tied together at the electrical service panel. Now think about what would happen if the scope test probe ground lead was connected to DC- without an isolation transformer. This would basically short out D4 and put D2 directly across the line (among other things). Not good. With an isolation transformer for the power supply, there will be no fireworks. However, an isolation transformer for the scope will not help unless it has an isolated ground, or the scope ground is disconnected.

Disconnecting the scope from ground allows its case to float which will prevent the melt-down but is EXTREMELY DANGEROUS since the entire scope cabinet is effectively connected to the power line. You (or someone else not familiar with your foolishness) may casually touch or lean against the scope cabinet and be thrown across the room if it is a lucky day or worse. Don't do it! Invest in an isolation transformer. It is very cost effective insurance.

No solution is perfectly safe as there will always be potentially lethal combinations of terminals inside high power or high voltage equipment, but the idea is to minimize risks. Using an isolation transformer for the equipment being serviced along with a battery powered scope or one with ground leads that are NOT directly connected to Earth Ground and its case is best.

However, many, if not most scopes, tie the ground leads and case to Earth Ground.

• When using these for equipment with 2-wire cords like most TVs, using an isolation transformer on the equipment is acceptable. But this still means that when the scope ground is connected inside the equipment, the scope case is still a shock hazard with respect to live points inside the equipment.

• For equipment with 3-wire cords like PC power supplies and high-end A/V equipment, using separate isolation transformers for both the equipment being tested and the test equipment may be desirable, but this would require isolating the test equipment ground(s) as well. And even then, the scope case may still be a risk as noted above.

One test method that potentially eliminates the issue of the scope ground entirely is to use the A-B setting available on most 2 (or more) channel scopes. However, the isolation transformer is still desirable for safety, and may be needed eliminate the large (identical) voltage swing which would be present on both probes, possibly affecting the measurements since the common mode rejection of the vertical amplifiers in many scopes may not be very good.

In the end, developing proper work habits like keeping one hand in your pocket when dealing with high voltage or line voltage, changing test setups only with power off, and confirming that large capacitors are discharged before touching anything, are at least as important as isolation transformers and other safety gear in minimizing risks.

Basic Ancillary Equipment

• TVs: VHF and UHF antennas and/or VCR or other video source with both RF and baseband (RCA plugs) outputs.

• VCRs: a small TV (preferably color but a monochrome TV will suffice for many tests) and/or NTSC/PAL video monitor, antenna, known good video tapes at both SP and SLP speeds. Also, a couple of blank cassettes for record tests.

• Camcorders: same as VCRs but in addition, a test chart, tripod, and lamps for indoor testing.

• CD and Laserdisc Players: - a garbage CD and test CD (or laserdiscs). A garbage disc is one you do not care about if it gets scratched. A test disc does not need to be an official (and expensive) test disc - any known good disc will do for most tests. The garbage CD can even be an outdated CDROM - an audio CD player will often read the directory of a CDROM just like an audio CD.

  Special cut-down miniature test CDs can be made to view the lens motion while focusing and to permit access to adjustments blocked by normal CDs in many portable players. See the document: Notes on the Troubleshooting and Repair of CD Players and CDROM Drives for details.

  An IR detector will be needed to confirm laserdiode operation.

  An audio amplifier with speakers or headphones will be needed for the audio tests, or headphones if the unit has a headphone jack. A TV or video monitor will be needed for Laserdisc video tests.

• Audio Equipment - a set of known working stereo components consisting of at least a tuner, amplifier, and speakers. Headphones are also useful. For most purposes, an inexpensive setup is preferred since there is no telling what kind of abuse it may need to endure during troubleshooting. I suppose that a turntable may even be needed occasionally. A couple of prerecorded audio cassettes are handy when testing tape decks. One of these should have a tone of known frequency recorded on an accurately calibrated deck for setting tape speed. Also, a couple of blank cassettes for record tests.

• Microwave Ovens - a cup of water for a load. You don't need special microwave approved water - tap water will do :-) A thermometer for power tests. Neon or incandescent bulbs with their leads shorted together can serve as microwave detectors inside the oven (though these may not always survive for very long).

• PCs and components - a working basic PC is useful to serve as a testbed for trying suspect components. I use an old 286 mainboard with just enough to boot from an old hard drive. A set of known working basic PC peripheral boards is useful - SA, IDE and MFM HD and FD controller, I/O ports, sound card and speakers, 5-1/4" and 3-1/2" floppy drives, etc. A spare power supply - even one that is not an exact mechanical match - is also handy for testing. An old laptop (commonly used as a door stop) is useful for testing printers on location.

• Computer Monitors - a test PC is useful as a video source. Of course, it will need to support whatever scan rates and video types the monitor is designed to accept. Programs are available to display purity, convergence, focus, color, and other test patterns.

• Telephones, answering machines, faxes - a phone line simulator is useful for initial tests. For many purposes, a DC power supply or battery and 600 ohm resistor will be all you need. A pair of normal phone lines will of course also work but you will need to provide jacks where you are working and access (which may be difficult with teens in the house).

Incredibly Handy Widgets(tm)

• Series light bulb for current limiting during the testing of TV sets, monitors, switching power supplies, audio power amplifiers, etc. I built an outlet box with two outlets wired in series, switch, and indicator. A lamp or other load can be plugged into one outlet and the device under test into the other. Clearly label the special outlet box so you (or someone else) will not attempt to use it for other purposes!

  A typical schematic is shown below:

  
            H o-------/ ---+-------+
                   Power   |       | H     N
                   Switch  /       +--|   |--+  Current limiting load
                           \                 |
                       47K /            o G  |
                           \                 |
                           |       +---------+
                          +++      | H     N
                     NE2H |o|      +--|   |--+  Device under test
                    Power |o|                |
                    Light +++           o G  |
                           |            |    |
            N o------------+-----------------+
                                        |
            G o-------------------------+
  
  

  Note: Ground connections normally not used for equipment likely to be tested using this device.

  See the repair guides for specific equipment for more details on the use of the series light bulb.

• Capacitor discharge tool. This device provides a safe and low stress (for your spouse - no zap) way of discharging the capacitors found in TV sets, monitors, microwave ovens, electronic flash units, etc. An indicator can easily be built in as well to provide a visual confirmation as the voltage decays.

  Safety note: always double check that capacitors are fully discharged with a voltmeter before touching any high voltage terminals!

  See the document: Capacitor Testing, Safe Discharging and Other Related Information for additional information.

• Video cassette cheater. This is the shell of a VHS or Beta cassette with all of the innards removed and most of the top and bottom cut out to permit access to the reel spindles and other rotating components of a VCR during operation. You can also purchase these at grossly inflated prices.

  See the document: Notes on the Troubleshooting and Repair of Video Cassette Recorders for additional construction details.

• Degaussing coil. Make or buy. The internal degaussing coil salvaged from a defunct TV doubled over to half it original diameter to increase its strength in series with a 200 W light bulb for current limiting, (use the series light bulb widget for this), fuse, and momentary switch will work just fine.

  See the document: TV and Monitor CRT (Picture Tube) Information for additional information on CRT magnetization and degaussing techniques.

• Tape head demagnetizer. This could just be a coil wrapped around a common nail with its end protected with tape. Connect to low voltage AC. However, these are so inexpensive that you should just buy one.

  See the documents: "Notes on Troubleshooting and Repair of Audio Equipment and other Miscellaneous Stuff" and "Notes on Troubleshooting and Repair of Video Cassette Recorder (VCR)" for additional information on tape head demagnetizing.

  Caution: do not use a demagnetizer on video heads unless specifically designed for them. Some are strong enough to damage the fragile ferrite cores. Video heads generally do not require demagnetizing anyhow.

• IR detector. This can be a photodiode/LED circuit or IR sensitive card. Use for testing remote controls, IR LEDs in photosensors, and CD laserdiodes.

  See the document: Notes on the Troubleshooting and Repair of Hand Held Remote Controls for construction details.

• Flyback tester. I use a 12 V chopper with a 10 turn coil to excite the flyback under test. This will identify most primary and secondary short type faults under near-operating conditions.

  See the document: Testing of Flyback (LOPT) Transformers for additional information.

• High voltage probe for your multimeter. This will come in handy when testing the high voltage circuits of TVs, monitors, and microwave ovens (though extreme care will be needed, particularly with the latter). See the document: Simple High Voltage Probe Design for details on basic high voltage probes you can construct from (relatively) readily available parts. These will be satisfactory for DC voltages but compensation to get any kind of high frequency response can be tricky. However, that will handle most consumer electronics needs.

• Not-so-fantastic current probe. When diagnosing TV and monitor deflection problems, a current probe may be desirable to view the current waveforms in the yoke and flyback. You cannot view the high voltage signals without a high frequency high voltage probe.

  If you have a current probe for your scope, this can be used to monitor the various current waveforms. I have used my Tektronix current probe to view the yoke current on TVs. The rendition of the horizontal deflection current waveform is quite good. However, the vertical suffers from severe distortion due to the low frequency cutoff of this probe.

  You can build a not-very-fantastic (but quite usable) current probe using a split ferrite core of the type used on keyboard and monitor cables (preferably one that snaps together). The following will work:

  • Wrap seven turns of insulated wire around one half of the core.
  • Solder a 2.2 ohm resistor across the two leads to act as a load.
  • Connect to the vertical input of your scope via a coaxial cable or probe.

  You can experiment with the number of turns and load resistor value for best results.

  To use your fabulous device, insert one and only one of the current carrying wires inside the ferrite core and clamp the two halves together.

  For a typical TV horizontal deflection yoke, this results in about a .3 V p-p signal. The shape was similar to that from my (originally) expensive Tektronix current probe. Enjoy the show! Due to its uncompensated design, this simple probe will not work well for low frequency signals.

• Quick and dirty curve tracer. A curve tracer is useful for displaying the I-V characteristics of semiconductor and other devices. See the sections on curve tracer design in the document: Basic Testing of Semiconductor Devices.

  There is info on useful devices for your scope that you can construct in about 10 minutes. These won't replace a fancy Tek 576 but may be all you need (or at least can justify on a finite budget).

• Handy-dandy phone line tester. The inexpensive variety is just a pair of LEDs in series with a resistor for each line attached to an RJ11 connector. However, this is much more convenient than fumbling with a multimeter! You can buy one at Radio Shack (about $7) or easily build your own. See the document: Notes on the Troubleshooting and Repair of Audio Equipment and Other Miscellaneous Stuff, specifically the section: "Handy-dandy phone line tester" for details.

• High voltage diode and neon bulb tester. This is a line powered low current voltage doubler producing up to about 300 VDC to test (in conjunction with a Variac and multimeter) for reverse blocking of high voltage rectifiers, diodes, and ratings of high voltage zeners, neon and other small discharge lamp characteristics, and so forth.

  WARNING: Use an isolation transformer with this device since it is line connected without isolation. The maximum sustained (short circuit) current is only 4 or 5 mA but this is still enough to be dangerous so respect it even with the isolation transformer!

  
                       C1                   D2
             AC H o----||--------------+----|>|----+-----+----o +DC
                      .2uF             |  1N4007   |     |
                      250V       D1    |           |     /
                             +---|>|---+       C2 _|_    \ R2
                             | 1N4007        .5uF ---    / 5M
                             |               400V  |     \
                       R1    |                     |     |
             AC N o---/\/\---+---------------------+-----+----o -DC
                      3.3K
                      
  

Cheater Cords

Exactly why this is no longer done except to save money isn't quite clear. Chassis of modern equipment like TVs, computer monitors, microwave ovens (especially microwave ovens) are very dangerous. Perhaps the manufacturers figure that at least for the first two, not using vacuum tubes, most of their voltages are lower. More likely, since they provide the warning "no user serviceable parts inside", they figure that they can't be sued and it is isn't worth spending the 10 cents for the extra plug. :)

Where your equipment actually has this sort of interlock, it is usually possible to pop off a retaining clip and use the original cord for this purpose. Just make sure you understand the safety issues. Modern devices may not have several hundred volts sprinkled all over the chassis like those using vacuum tubes, but there may be non-isolated line voltage, 25 kV or more for the CRT, or 5,000 V at AMPs in a microwave oven. You can be just as dead from these!

Monitoring Current Consumption from Batteries

(Portions from: Raydon Berry (rayberry@pt.lu).)

Take a small piece of stiff plastic (e.g., as used in blister packs) and attach strips of self adhesive copper or aluminum foil to both sides. Shape one end of the strip into a sort of finger, narrow enough to slip between the AA or AAA batteries or batteries and the contact when they are installed in the holder. If the foil is copper, wires can be soldered to each side at the other end. If aluminum, cut away a portion of the foil in opposite locations on both sides so clip leads from a multimeter can be attached without shorting.

This device is used (frequently by me) for checking the current consumption of all battery powered equipment - it's very simple and very cheap.

For example, with remote controls, insert between batteries and put the multimeter on a range of about 25 mA and when you press each button, the code being sent will show up as a wagging needle on a VOM or an average current for a DMM. If the ceramic filter or the IR diodes have failed, the current remains very low, but if OK, you should see pulses of 5 to 10 mA.

For other devices, select an appropriate range. It might not be a bad idea to check new/working equipment as well to obtain a "signature" of health which is recorded on a slip of paper glued inside the battery compartment. Then, if the device should fail, a comparison can easily be made.

Miscellaneous

• Clip leads. Like woodworking clamps, you can never have too many of these.

• Patch cords for audio, video, and telephone interconnection.

• Parallel (Centronics) printer, serial (breakout box desirable), other computer cables.

• Insulating sheets - for separating circuit boards when removed from the chassis. These can be cardboard, fiberglas, plastic, etc.

• Insulating sticks - for prodding to locate intermittents.

• Small parts tray and container. I always use a film canister or pill bottle for storing the screws, washers, and springs removed during disassembly. An icecube tray or egg carton makes a handy parts bin for temporary storage of small parts while you are working.

Making a Bench Power Supply from a PC Power Supply

• Typical (but not always) color codes for PC power supplies:

  Red: +5, Yellow: +12, Black: Gnd (Probably case as well).
  White: -5, Blue: -12, Orange: Power_good (output).

  (Some newer supplies may have a +3.3 output as well which may be green).

• PC power supplies (as well as most other switchers) need a minimum load on +5 and possibly on +12 as well. An amp (e.g., 5 ohms on +5) should be enough.

  I use an old dual beam auto headlight. It adds a touch of class as well to an otherwise totally boring setup :-). You can also use auto tail light bulbs or suitable power resistors or old disk drives you don't really care about (you know, those boat anchors).

• There are no sense lines. There is a 'Power_Good' line which is an output from the power supply to the mainboard and can be ignored unless you want to connect it to an indicator to let you know all the outputs are within specs (it may need a pullup and I don't know its drive capability).

• Pinout for the standard PC and clone connector (some companies like Compaq do NOT use this type of connector, however.). Black (Gnd) wires together for the P8 and P9 connectors when installed to mainboard.

        J8: Pin 1 = Power_Good   J9: Pin 1 = Gnd
        Pin 2 = +5               Pin 2 = Gnd
        Pin 3 = +12              Pin 3 = -5
        Pin 4 = -12              Pin 4 = +5
        Pin 5 = Gnd              Pin 5 = +5
        Pin 6 = Gnd              Pin 6 = +5
  

  Note: for an XT only, J8-Pin 1 is Gnd, J8-Pin 2 is no connect.

• The peripheral connectors are: Pin 1: +12, Pin 2 and 3: Gnd, Pin 4 = +5.

Soldering and Desoldering Equipment and Techniques

Solder is Not Glue

However, the purpose of solder is not to physically anchor connections - they must be mechanically secure first to assure reliability. When properly done, solder actually combines with the clean metal surface of the wires, pins, and terminals assuring a low resistance connection.

While there are several conditions must be satisfied to achiev good reliable solder connections, with a little practice, soldering will become essentially automatic and you will know immediately when the results are satisfactory.

There have been entire handbooks written on proper soldering technique. Organizations like NASA take this seriously - after all, a service call to the one of Jupiter's moons would be quite costly!

Aditional information on soldering techniques and equipment can be found at:

• The Basic Soldering Guide

CAUTION: You can easily turn a simple repair (e.g., bad solder connections) into an expensive mess if you use inappropriate soldering equipment and/or lack the soldering skills to go along with it. If in doubt, find someone else to do the soldering or at least practice, practice, practice, soldering and desoldering on a junk unit first!

Soldering Equipment

• A low wattage (25 W) iron for delicate components including discrete semiconductors, ICs, other small parts).

• A medium wattage (40-50W) iron for heavy duty circuit board work including power components, power plane connections, and large transformers).

• A 100-140 W soldering gun for chassis connections.

I consider fine gauge rosin core solder (.030 or less) to be best for most applications (e.g., Ersin Multicore).

• Desoldering pump - SoldaPullit or similar 'solder sucker' for removing components easily and usually nondestructively. SolderWick is also handy for cleaning up desoldered connections.

Soldering Techniques

However, there are times where soldering is more convenient. Use of the proper technique is critical to reliability and safety. A good solder connection is not just a bunch of wires and terminals with solder dribbled over them. When done correctly, the solder actually bonds to the surface of the metal (usually copper) parts.

Effective soldering is by no means difficult but some practice may be needed to perfect your technique.

The following guidelines will assure reliable solder joints:

• Only use rosin core solder (e.g., 60/40 tin/lead) for electronics work. A 1 pound spool will last a long time and costs about $10. Suggested diameter is .030 to .060 inches for appliances. The smaller size is preferred as it will be useful for other types of precision electronics repairs or construction as well. The rosin is used as a flux to clean the metal surface to assure a secure bond. NEVER use acid core solder or the stuff used to sweat copper pipes! The flux is corrosive and it is not possible to adequately clean up the connections afterward to remove all residue.

• Keep the tip of the soldering iron or gun clean and tinned. Buy tips that are permanently tinned - they are coated and will outlast countless normal copper tips. A quick wipe on a wet sponge when hot and a bit of solder and they will be as good as new for a long time. (These should never be filed or sanded).

• Make sure every part to be soldered - terminal, wire, component leads - is free of any surface film, insulation, or oxidation. Fine sandpaper or an Xacto knife may be used, for example, to clean the surfaces. The secret to a good solder joint is to make sure everything is perfectly clean and shiny and not depend on the flux alone to accomplish this. Just make sure the scrapings are cleared away so they don't cause short circuits.

• Start with a strong mechanical joint. Don't depend on the solder to hold the connection together. If possible, loop each wire or component lead through the hole in the terminal. If there is no hole, wrap them once around the terminal. Gently anchor them with a pair of needlenose pliers.

• Use a properly sized soldering iron or gun: 20-25 W iron for fine circuit board work; 25-50 W iron for general soldering of terminals and wires and power circuit boards; 100-200 W soldering gun for chassis and large area circuit planes. With a properly sized iron or gun, the task will be fast - 1 to 2 seconds for a typical connection - and will result in little or no damage to the circuit board, plastic switch housings, insulation, etc. Large soldering jobs will take longer but no more than 5 to 10 seconds for a large expanse of copper. If it is taking too long, your iron is undersized for the task, is dirty, or has not reached operating temperature. For appliance work there is no need for a fancy soldering station - a less than $10 soldering iron or $25 soldering gun as appropriate will be all that is required.

• Heat the parts to be soldered, not the solder. Touch the end of the solder to the parts, not the soldering iron or gun. Once the terminal, wires, or component leads are hot, the solder will flow via capillary action, fill all voids, and make a secure mechanical and electrical bond. Sometimes, applying a little from each side will more effectively reach all nooks and crannies.

• Don't overdo it. Only enough solder is needed to fill all voids. The resulting surface should be concave between the wires and terminal, not bulging with excess solder.

• Keep everything absolutely still for the few seconds it takes the solder to solidify. Otherwise, you will end up with a bad connection - what is called a 'cold solder joint'.

• A good solder connection will be quite shiny - not dull gray or granular. If your result is less than perfect reheat it and add a bit of new solder with flux to help it reflow.

Desoldering Techniques

For stubborn joints or those connecting to the power planes (surface or multilayer boards), you may need to add some fresh solder and/or flux and then try again. Generally, if you only get part of the solder off the first time, repeated attempts will fail unless you add some fresh solder.

Other approaches that may be used in place of or in addition to this: Solder Wick which is a copper braid that absorbs solder via capillary action; rubber bulb type solder pumps, and motor driven vacuum solder rework stations (pricey).

(Portions from: Pat Brunner (Brunner@ieee.org).)

I have used a SoldaPullet for 30 years but found an inexpensive improvement. Add a 1 inch length of silicone tubing (or something else that won't be damaged by the heat, 1/8" ID x 1/4"OD) over the SoldaPullet tip leaving 3/16" to 1/4" extending past the tip. This absorbs the downward force when the SoldaPullet is fired reducing damage to the PCB, provides a better seal around the component lead so it's often possible to clear a hole in one operation that might otherwise require several, and it prevents the plastic tip of the SoldaPullet from being damaged.

Nick's Comments on Successful Desoldering Techniques

(From: Nicholas Bodley (nbodley@tiac.net).)

A few points to keep in mind...

Try to get cutters that will let you snip individual leads on the IC. Get tool catalogs! I like Contact East, in the USA; not sure about Canada. Jensen, in Arizona, I think, tends to be costly.

If you snip all the leads on one side, you can bend the IC back and forth to break the other side free, but be sure to do the bending next to the plastic (it's harder to do there).

When you cut the IC leads, do your best to leave most of each lead sticking up above the surface of the board.

Set your iron to about 770 deg. F (400 deg. C). (This assumes a modern soldering station with a temperature control, and a relatively-slender tip.) Be sure that the tip is clean and shiny and properly tinned. Any oxidation is just no good. (DON'T file modern plated tips! You'll remove the plating!). Be fanatical about ensuring that the tip always idles with a decent coating of solder.

Hotter temps run a real risk of spoiling the adhesive bond that holds the copper foil to the board. DO NOT use a higher temp to make up for an improperly-tinned tip!! (You might need a higher temp for holes in the middle of ground planes, however. These will sink the heat away effectively; but do those separately.)

You must get each pad hot enough to be well above the melting point, so that the cold air won't make the solder resolidify when you slurp it up.

To transfer enough heat, you must have a fillet of solder between the tip and the pad. If necessary, add a bit of solder to ensure this!

After hitting these points so hard, I'll relax and say that you'll really do better if you remove each lead stub individually with assembly tweezers (AA style are good) or thin needle-nose pliers.

Once they're all out, then you need to be concerned about heating the pads enough. Now you can desolder. The other messages in this post have good advice on that.

You need to maintain your desoldering tool, too. It might not have good vacuum if ignored.

It's tricky to hold the iron on the pad while getting the nozzle close enough, but a decent desoldering tool will work if tilted somewhat to let the tip contact the pad.

If a hole doesn't open, but some solder has been slurped up, you could try good solder wick (Solder-Wick (Soder-Wik?) brand is good); it can sometimes pull up solder from underneath by capillary action. (I didn't believe this until it happened!) Poor solder wick isn't fluxed sufficiently, or might be subtly corroded. It should soak up solder like a sponge.

It might be quicker to refill the hole with a bit of solder and repeat; there could be a good blob of it on the other side, which you might, or might not, be able to get to.

(If you can get to both sides, and have five hands, you could apply heat to one side, let the tip dwell for a few seconds to melt all the solder, and slurp from the other side.)

If things become messy, apply liquid flux (seems not to be too easy to find in small quantities; I use a flux pen, which seems not overpriced). Reheat the pad, and the flux should do a great job of tidying things up. It tends to let capillary action make the holes open wider, when most of the solder has been picked up.

I think it's well worth the effort to cut the leads free from the IC body and remove them one at a time, then go over the pads a second time to remove the solder.

I have very recently removed a 16-pin DIP twice from a location without damaging the pads at all by these principles.

It's much harder, or impossible, to do good work with poor tools. Do try to get good tools, and learn to take care of them.

Soldering Pins in Plastic Connectors

One approach that works in some cases is to use the mating socket to stabilize the pins so they remain in position as you solder. The plastic will still melt - not as much if you use an adequately sized iron since the socket will act as a heat sink - but will not move.

An important consideration is using the proper soldering iron. In some cases, a larger iron is better - you get in and out more quickly without heating up everything in the neighborhood.

Comments on Repairing Damage to Printed Circuit Boards

• Traces may be damaged due to poor soldering or desoldering techniques or by acting as fuses due to short circuits. Where there is just a gap in a trace, it may be possible to scrape off any protective coating (the solder mask) and then soldering a bare jumper wire to bridge the gap. DO NOT just put a blob of solder there - it won't last. However, it is often better to remove the remains of the trace entirely and solder a wire between the two end-points.

• When components overheat, they can also damage the PCB material underneath them. If the PCB is just slightly discolored, then probably it can be cleaned up and reused. This will often happen under hot components even with properly functioning equipment after many years of operation and doesn't cause problems.

  But if there is actual damage to the board material itself, then the carbon that is present and can't be removed will result in a conductive path which may result in circuit failure or erratic behavior. It would be best to replace the entire PCB if possible. But a more realistic alternative is to cut out the bad section and build the missing circuitry on a separate prototyping board.

Supplies and Parts

Lubricants, Cleaning Agents, and Other Liquidy or Slimy Stuff

• Light oil such as electric motor oil or 3-In-One. WD40 may be useful for cleaning or freeing rusted screws but it is not a general purpose lubricant despite what is claimed on the label.

• Light grease suitable for fine electronics - must be plastic-safe.

• Isopropyl alcohol (91 % medicinal or better preferred though rubbing alcohol (70 percent) can be used in a pinch as long as it doesn't contain any additives).
  • Q-tip swabs (you may know them as cotton buds) for cleaning of everything BUT the video heads on VCRs and other helical scan tape transports.

  • Chamois covered head cleaning sticks for video heads.

  Note that sometimes plain water will work better for sugar based coatings. Tape head cleaner can be used for head cleaning as well.

• Contact cleaner in spray can. This is used for switches and relays.

• Control cleaner in spray can. This is used for potentiometers and will probably include some type of non-drying lubricant.

• Tuner cleaner and lubricant in spray can. The stuff sold by Radio Shack works fine.

• Degreaser in spray can. Use with care around plastics.

• WD40 in spray can. NOT for lubrication in most cases. However, WD40 is an intermediate strength solvent that comes in handy for cleaning, removing labels and label goo, coating tools to prevent rust, etc.

• Liquid flux for helping in tough soldering and desoldering jobs.

• Flux remover. Isopropyl alcohol will work but there are also spray cans of this stuff.

• Silicone heat sink compound. A little goes a long way. You don't need to goop it on - just the thinnest film to fill voids. Here are some numbers:

  (From: Asimov.)

  Thermal resistance (°C/W) for silicone heatsink compound:

      Insulator           Without   With
     ------------------------------------
      None                 0.20     0.10
      Anodized Aluminum    0.40     0.35
      Mica                 0.80     0.40
      Teflon               1.45     0.80
   

Note that using no insulator is always better than one with heatsink compound for these materials (no data on BeO which may be the exception).

(From: Gavin Parrish (the_big_geez@ameritech.net).)

Kano Labs makes a number of exceptional products which are only available directly through them. They are not cheap, but all that I have tried have met or exceeded my expectations. Their premier product is "KROIL" a penetrating oil that breaches a space as small as one millionth inch. No fooling! Throw away that WD whatever-its-called stuff. If it's stuck, this will unstick it.

While they have a lot of really big industrial customers, they give attentive service even if you only buy 1 can. The only drawback is they keep sending you somewhat amusing flyers every month or so. You already get a lot of this so it's no big deal.

For info or ordering contact: (what? no URL?!): Kano Laboratories, 1000 Thompson Ln., Nashville, TN 37211-2627. Phone: 1-615-833-4101, Fax: 1-615-833-5790.

(The above is not a paid promotion, merely data I hope you find useful.)

(From: Rich Grise (richardgrise@yahoo.com).)

Which solvent to use depends on what you're trying to dissolve. For a something like a cruddy motor, I'd try, in order from least aggressive up:

1. Isopropyl alcohol - good on most oils and greases, fairly innocuous chemically.

2. Ethyl alcohol - as good a solvent, or better than isopropyl, but much too valuable as a beverage.

3. Methyl alcohol - don't even touch this crap - if you even just get it on bare skin, it can blind you. (Actually, this is an extreme position, methyl alcohol is mainly dangerous if ingested. --- Sam.)

4. Naphtha (lighter fluid) - the only solvent I've ever seen that can get chewing gum out of your hair. Not too good on aliphatic greases, however.

5. Mineral spirits or turpentine - still flammable, makes good paint thinner, but seems to leave a greasy residue when used for cleaning.

6. Toluene/xylene - excellent cleaner, but it could attack the insulation on the windings. Breathing the fumes can cause a sort of intoxication that I think isn't very good for you.

7. Acetone/MEK - MEK is less volatile, but still quite aggressive. Very flammable, but evaporates completely without residue. Acetone is the only thing I've ever seen that can dissolve acrylic plastics like Plexiglas.

The chlorinated/fluorinated solvents sit somewhere in the middle of the range - someone else pointed out the difference between trichloroethylene and trichloroethane; I guess TCA is much friendlier than TCE - but we used them in the Airforce to clean up hydraulic fluids that nothing else would even touch.

I've heard that Vaseline makes a superb lubricant for bike bearings; it also makes a reasonable vacuum seal, and it's incredibly tenacious - one day, I used it on a gasket, and when I needed to make a change, I couldn't find anything in the shop that would clean it up completely.

Don't use WD-40 as a cleaner; it gums everything up. I inherited an old Baudot teletype once and thought I'd clean it with a WD-40 spray. HAH! Spent the next week disassembling the thing and cleaning all the gunk off the intricate little parts with TCA or something. WD-40 is good for door hinges.

Carburetor cleaner is a mixture of solvents in a spray can which may include acetone, toluene and methanol but it's extremely flammable and it seems to wash greasy dirt away as if it weren't even there.

Adhesives

• Two part Epoxy. Epoxy is one of the strongest and most versatile all around adhesive and bonds well to most materials except some plastics. I recommend separate tubes, not the combined syringe type. With tubes, it's much easier to get exactly what is needed. The syringes invariably dispense about 10 times the desired quantity and then last for only a few uses.
  • Fast curing (5 minute) Epoxy is most convenient for quick repairs but may not be as strong as the slow curing (1/2 to 1 hour) type.

  • It is generally easier to do a neat job with clear Epoxy but white or metal types work as well.

  • Conductive (silver filled) Epoxy may be useful for repairing printed circuit board traces and remote control pads but is no substitute for metal wires.

  • There is also special Epoxy for plastics which may form a stronger bond to certain types of plastics than normal Epoxy.

• Industrial quality cyanoacrylate like Loctite 401. The common types (Crazyglue, Superglue) work but stick to everything you don't want stuck together and the tubes never seem to keep the unused portion in decent condition. Loctite 401 comes in a nice bottle with applicator and proper recloseable top. This is probably best for instant repairs.

• General purpose adhesive like Duco Cement.

• Semi-flexible adhesive like windshield sealer.

• Flexible adhesive like weather strip cement or silicone sealer or RTV. Note: some types may be corrosive to metals upon curing - test first. One example of a suitable product would be Dow Corning #736 RTV though I don't know first hand if it is acid-free.

• Solvent type plastic cement or plastic model cement.

• Rubber cement.

• Plastic electrical tape.

• Masking tape.

• Clear plastic tape.

Electronic Sealers and Potting Compounds

Ordinary silicone window and bathtub caulk has the right mechanical and electrical properties (tough, flexible, excellent insulator especially for high voltage), but it secretes acetic acid upon curing and this may damage the electronic circuitry (but not always the case). Some types claim to be safe for this or that (e.g., aluminum) but unless it states specifically that it is safe for electronics, use at your own risk.

(From: Ralph L. (ralphl@keycomp.net).)

You can also use an RTV that is safe for oxygen sensors that are used on most computer controlled cars. It does not produce that acetic acid (vinegar smell) during the curing process and will not harm electronics.

(From: Greg Szekeres (gjs@prophet.pharm.pitt.edu).)

Yes, Permatex Ultra Blue is safe, available at most auto parts stores. I have also been using polyurethane instead of silicone, although is has problems with some materials.

(From: RadMan (radcom@comnet.ca)).

Some agents require UV to cure, some need heat. You can also try Miller-Stevensen 907 available at Future/Active, and it pots with a heat gun very fast (30 minutess).

(From: Bob Wilson (rfwilson@intergate.bc.ca).)

Dexter makes Hysol Epoxy which is a potting compound that totally encapsulates the circuits. There are easily available commercial coloring compounds intended for this purpose, and are available from the supplier of the Epoxy. An alternative is to mix some laser copier toner (dry powder) with the epoxy if making it opaque is desired.

Mind you, all that potting does as a means of security, is to keep he amateurs out. Depotting an electronic assembly is pretty easy. All that is needed is judicious application of a small welding torch flame to locally heat the epoxy above its glass temperature (whereupon it becomes rather "crunchy" and easy to remove), and a little patience.

(From: Brian Symons (brians@mackay.net.au).)

The products normally safe to use are labeled "neutral cure" or at least they are here in Australia.

Any acid cure product is certainly dangerous around electronics. I cam across some PCB's that had had the wires glued in place by a run of acid cure silastic across the board.

When looking for the fault, I peeled up the silastic and found every track under the silastic was completely eaten away.

BTW. Over here, It is quite common for ovens to have a from glass viewing window that is glued in position with a silastic material that can handle the high temps.

When a warrantee guy ordered in a tube of the silastic, they supplied a tube of the silastic that is available here at car parts suppliers and service stations to repair windscreen seals. They were only charging about eight times the price though. This silastic is a black product. I have used it successfully for oven glass repairs for several years.

Electronic Parts

A good source for many of the basic parts is dead equipment - their organs can live on at your workbench. Parts like small resistors are so inexpensive that this doesn't warrant a lot of time. However, power resistors, potentiometers, power semiconductors, some ICs, etc. are well worth saving. Used electrolytic capacitors will generally still be functional but these do deteriorate with time and heat so testing them first and avoiding the use of really old ones for the permanent repair is probably wise. The majority of my parts inventory is from salvage. Think of them as 'pre-owned burned in components' :-).

• Resistor assortment. A variety of resistor packs for digital termination.

• Potentiometers (variable resistors), assorted values.

• Capacitor assortment - ceramic and electrolytic. Large high voltage electrolytics for power supplies.

• Rectifiers - 1N4007s for primaries of power supplies. Microwave oven rectifier. Fast recovery rectifiers - for switching supplies.

• Diodes - 1N4148 signal diodes.

• Transistors (bipolar): small signal, medium power, high power audio, and horizontal output transistors. Obviously, this list could get quite long. A few basic types will suffice in a pinch.

• Fuses - 3AG size (1-1/4"x1/4") - .5, 1, 2, 3, 5, 10 amp. You can always solder these across the smaller 5x20 mm fuses often found in consumer equipment these days.

• LEDs and indicator lamps.

• Wire: assorted colors of #24, #18, and #14 stranded and solid insulated wire. 75 ohm coax for video. Shielded cable for audio. Fine wire (e.g., #30, bare and insulated) for PCB repairs.

• Assorted small switches - toggle, pushbutton, etc.

• Line cords, plugs, and other electrical components.

• Lamp sockets, single and three-way switch/sockets, plugs, etc. for small appliance repair.

• Various jacks and plugs such as RCA, phono, F, BNC, etc.

• Small loudspeakers, headphones.

• etc., etc., etc.

Mechanical Parts

• Hardware assortment including English machine screws and nuts, Metric machine screws (mostly for replacement use, and Metric nuts are rare), and flat and lock washers.

• Plastic split washer assortment. Despite dire warnings to the contrary, these can often be reused. However, they are easily lost.

• E-clip and C-clip assortment. These can be reused but very often go 'pling' into never-never land when removed.

• Spring assortment.

• Several thicknesses of steel wire.

• Various bits of plastic, wood, and metal to fabricate splints or other emergency repairs.

• Dial cord material.

Plastic Parts Repair

Note that there are quite a variety of what we call "plastics". An adhesive that bonds with extreme strength to one may not even stick at all to another. (Nylon and polyethylene are difficult to glue; styrene is easy.) This is especially true of the 'welding' adhesives like MEK.

However, using the most appropriate glue can make a very significant difference:

• MEK (Methyl Ethyl Ketone) is the stuff in plastic solvent used for 'welding' styrenes. This results in a truly adequate repair only under very special conditions (which I've yet to encounter).

• Plastic model cement contains allyl Isothiocyanate (oil of mustard, huh?), and is good for styrene and acrylic plastics. Not recommended for polyethylene or phenolic plastics or for styrofoam (which it will eat).

• Duco Cement(tm) and similar all purpose glues are decent for many plastics including phenolics. Windshield sealer is similar but results in a semi-flexible repair.

• Tenex 7R is recommended for joining dissimilar plastics.

• SuperGlue(tm) and its clones (Cyano-acrylics) are only good on some plastics and only where the fracture is clean with a perfect fit upon reassembly. However, they are excellent for sticking thumbs to foreheads. :)

WARNING: The vapors from all of these adhesives are harmful to health if inhaled. Work only in a well ventilated area.

CAUTION: Spills from some of these will also damage paint and other plastic surfaces (including eyegless lenses!) even if wiped up immediately.

• RTV Silicon works well on a variety of plastics where a flexible repair is acceptable.

• Epoxies, wood glues, white Elmers glue, and library paste :) in general do not work well for plastics.

Where possible, I add reinforcement to plastic parts - either with plastic or metal. Or, fabricate all metal replacements. I've heard of people successfully adding bits of metal to replace plastic gear teeth. I have several clock radios with a mechanical clock where the little plastic pin in the number changing mechanism invariably broke after 5 years or so on all similar models. I replace them with a piece of steel wire (from a large paper clip) glued in place. This repair has worked for over 20 years. I bet the manufacturer saved a fraction of cent on each unit though! And, when someone forebly removed a paper jam on an HP DJ1000 printer and broke several pressure roller spring levers, stiff steel wire came to the rescue once again.

Sources of Information and General Comments

• The Internet, specifically the World Wide Web, has become THE preferred avenue for obtaining device datasheets and related information. While it may still be possible to obtain printed databooks, the convenience of typing in the part number to a search engine like Google and having its datasheet link appear almost instantly as one of the top 3 results cannot be overemphasized. This applies to virtually any widely used commercial discrete semiconductor or IC. Unfortunately, those with "house numbers" and more specialized ICs found in consumer electronics will probably not yield with this ease.

  For those of you without Web access at home or work, this may not sound like good news. However, libraries and other institutions are increasingly providing this service, and one can't hide from the future forever!

• The number and type of equipment that can be effectively and economically repaired is dwindling. VCRs, CD and DVD players, cell phones, pagers, and much other newer equipment is simply not designed to be repaired by anyone but the authorized service company - or not at all. Much A/V equipment is constructed so cheaply that it's lucky to last the warranty period. Compact high-tech devices are put together using surface-mount technology (SMT) and ICs that simply cannot be identified so anything beyond an obvious bad connection probably means it is junk. Absolutely NO service information is available in any form and the manufacturer, assuming they can be identified, couldn't care less about helping.

  PCs have been of this type for many years where anything beyond swapping modules is probably a futile exercise. Well, guess what? Devices lie digital set-top boxes, digital video recorders, video game consoles, and digital flat-screen TVs can be added to this list. Except, that they aren't going to use anything resembling standard modules like PCs still do to some extent. So, forget about achieving any significant success rate repairing this and similar equipment.

References

• Electronic Troubleshooting
  Don Matsuda, 1992
  ISBN 0-13-248055-7
  

Manufacturer's Service Literature

Identifying OEM Manufacturer - FCC Numbers

How do you determine the actual manufacturer? For most types of consumer electronic equipment, there is something called an 'FCC ID' or 'FCC number'. Any type of equipment that may produce RF interference or be affected by this is required to be registered with the FCC. This number can be used to identify the actual manufacturer of the equipment.

A cross reference and other links can be found at:

• FCC ID Numbers Cross Reference

Sams' Photofacts

Sams' Photofacts schematics and service literature are published by:

• Sams Technical Publishing
  5436 W. 78th St.
  Indianapolis, IN 46268-3910
  Phone: 1-800-428-SAMS
  Fax: 1-800-552-3910
  Email customercare1@samswebsite.com or customercare2@samswebsite.com
  Web: http://www.samswebsite.com/
  

These folders of service information have been published for over 45 years (I don't know for how long but I have a set for a 1949 portable 3 inch Pilot TV - about as portable as an office typewriter if you remember what one of those was like) and are generally the best most consistent source of service info for TVs, radios, some VCRs and other consumer electronics. There are some Computerfacts but the number of these is very limited. The VCRfacts are also somewhat limited and the newer ones tend to have strictly mechanical information.

Even if they don't list your model, they may have a folder for one using the same chassis so search by chassis number as well. Even if this doesn't help, there still may be a folder for models that are similar enough to be of value (though you really have to be in the library to be able to determine this by looking at the circuit diagrams or photos) so check out folders for other model numbers that are close to the one you really want.

Sams' Photofacts are often available (for photocopy costs) from you local large public library which may subscribe to the complete series. If not, a large electronic distributor can order the selected folder for you.

One advantage of the Sams' info is that it is compiled in a very consistent format so that once you are familiar with one model TV, it is easy to transfer that knowledge to any other. They provide waveforms at key locations and DC voltage measurements almost everywhere. Additional info such as IC pin to ground and coil resistances are often provided as well. The manufacturer's service manuals are generally not nearly as complete.

Note: I have heard that some of the Photofacts recently purchased directly from Sams Technical Publishing/Howard Sams have been poor photocopies with illegible scope waveforms rather than original printings. If this is the case, it is truly the end of an era and too bad. In any case, try to confirm the quality before you buy or get your info from the library.

Inside Cover of the Equipment

Microwave ovens do almost always have a schematic diagram of the microwave power generation circuitry pasted inside the sheetmetal cover. This will generally include at least the high voltage transformer, interlocks, rectifier, capacitor, and magnetron. Since most microwave oven problems are in these areas, this is all you are likely to need. The controller, especially electronic units, is often omitted or only covered superficially.

Additional Sources for Service Information and Manuals

There are now many many Internet sources for manuals and schematics of all types including those that are hard-to-find for vintage equipment. Some are free while others charge anywhere from a nominal fee to something ridiculous. Do your homework before spending money - most of those you likely need may be downloaded for free including those for major brands of test equipment, communications gear, and tube audio.

The links that used to be below have been removed since attempting to maintain two sets of nearly identical links (here and in my bookmark file), many with short half-lives, became unbearable. Therefore, please go to the "Manuals/Schematics" sections of Sam's Neat, Nifty, and Handy Bookmarks.

As of Fall, 2006, I have confirmed that all these Web sites for manuals and schematics are active. Note that since these sorts of sites come and go, I'd advise downloading and archiving whatever you might possibly need when you find them - don't just save the links. You may be sorry later!

(From: William E. Miller (eagle@trader.com).)

Besides the used Sams TV Repair Manuals I sell, here are a few good sources for various flavors of service manuals.

• A.G. Tannenbaum
  Electronic Service Data
  P.O. Box 386, Ambler, PA 19002
  Phone: (215) 540-8055
  Fax: (215) 540-8327
  E-Mail: k2bn@agtannenbaum.com
  Web: http://www.agtannenbaum.com/

  "Parts and Service Data, 1920s to the present". Lotsa stuff!

• Michelle Troutman
  47 No. Bain Street, Brewer, ME 04412-2007
  Email: mtroutm@michelletroutman.com
  Web: http://www.michelletroutman.com/

  Sams Photofacts and service manuals for older TVs, stereos, and radios, as well as test equipment, vacuum tubes, electronics books, and magazines.

  (From: Mike Kaufman (makaufman@jps.net).)

  "This is an excellent source for very reasonably priced repair manuals, especially out-of-date manuals,. Michelle's prices are on the order of $2.50 per manual plus $1.50 shipping - hard to beat."

• Marty Gasman
  Email: mgasman@tiac.net
  Web: http://www.tiac.net/users/mgasman
  

  He has a LOT of AUDIO service manuals for sale. Check his full list at his web site.

• Microtech - John Gallawa
  Email: microtech@gallawa.com
  Web: http://www.gallawa.com/microtech/
  

  "We will be happy to help anyone who needs a schematic or parts breakdown for virtually any make and model (commercial or residential) microwave oven."

• Mauritron Technical Services
  Phone: 01844-351694
  Email: mauritron@dial.pipex.com Web: http://www.mauritron.com/
  

  "Suppliers of Technical Books and Servicing Information to the television, video and computer repair trade"

• Manuals sometimes turn up at auctions - on-line (e.g., eBay) and others, as well as estate sales and the like, though these would hardly be regarded as a way of finding exactly what you want!

The U.S. Military has an extensive library of test equipment and related manuals, some of which are in the public domain:

(From: Dino (kl0s@cox.net).)

Go to: U.S. Army Logistics Support Activity. Select "Publications and Forms" which should get you to LOGSA Publications and Forums. Then select "Electronic Technical Manuals Online" which will roll you down to "Go to Electronic Technical Manuals Online". Click on this link which takes you to http://www.logsa.army.mil/etms/online.htm. If you accept their terms, click on "I accept" which takes you to http://www.logsa.army.mil/etms/welcom1.htm Choose "Enter the Site" [Note the disclaimer that you have to login if accessing anything but public release manuals and that you have to have 128 bit encryption engaged. That should bring you to: http://www.logsa.army.mil/etms/find_etm.cfm. which is the search page; click on "TM Title Text" and enter, for example, "Tektronix" and scroll down to hit "Search" which should get you to: http://www.logsa.army.mil/etms/show_etm.cfm where if you scroll down and look CAREFULLY you'll find lots of material in .PDF format which you can then download.

You may have to go through this entire process to establish the fact that you accept their terms. There's probably a cookie in my system that lets me go straight to the search page. I've found a number of good references here for text equipment.

Canadian Schematics Source

(I have updated the contact information below so am not sure if everything applies to the new distributor. --- Sam.)

(From: John R. Hepburn (jhepburn@recorder.ca).)

I use a source in Canada for cheap schematics. I have to mention that they have limited coverage in the last while due to some O.E.M. holdbacks. There is nothing at all on monitors. It is:

• R.C.C. (Radio College of Canada)
  Available through: Just Radios
  Email: justradios@yahoo.com
  Web: http://www.justradios.com/
  

What they do cover is inexpensive, typically 5 schematics + data in one $19.50 manual ($14.00 U.S.). An example, I just received a manual the other day that I ordered to service a Sony VCR. It contained the following.

1. Citizen TV model JCTV-0204/JCTV-3097
2. Citizen VCR model JVHS-3931
3. Hitachi TV model CY07 C#G9LXU1M
4. Hitachi VCR model VT-M262A
5. Sony VCR models SLV-340/380/440/441

I suggest ordering their master index. They have 2 of them, pre-1973 and 1973 to present. You will need it for crossing anyway and it will give you a better idea what value their resources will be to you. Cost for an index is $5.00 (Can).

Reverse Engineered Schematics

• Bomarc Services
  P.O. Box 1113 Casper, Wyoming 82602
  Phone: 307-234-3488
  Web: http://bomarc.org/
  

I have no idea of their cost, reliability, quality, or accuracy but this type of source may be worth checking if you are desperate! One risk is that he wants $5 for catalogs of at most 3 categories from the following before you can order: audio, auto/air/marine, computer, detection, industrial, lighting, medical, phone, power supplies, radar, radio, security, tape/disk, telemetry, television, test equipment, time, toys & games, video, potpourri (misc).

Here is another company which has some reverse engineered schematics:

• Eagan Technical Services
  408 Northland Drive #304
  Mendota Heights, MN 55120
  Phone: 1-651-688-0098
  Web: http://www.eagantech.com/
  Email: dcarlson@eagantech.com
  

They have some PS/2 and other PC and monitor related schematics but not nearly the selections it would seem as Bomarc, above. I do not know anything more about this company.

Reverse Engineering Your Own Schematics

(From: Jeff Zurkow (jeff@atrox.com).)

Here's a trick I'm using for reverse engineering: Put the board on a color photocopier, set the copier for "mirror image", and make a copy. This gets you a top view of the underside, as if the board were transparent. You can tape a piece of drafting mylar over the copy, and draw in the topside components and traces with colored pencils. In fact, I sometimes use multiple mylars: top traces on one, components on another, component values on a third, and a final one on which I check off components and solder joints as I draw them on the schematic. It helps to have a light box :)

The layered drawing can also serve as a component-location key for future troubleshooting. Just assign new component identifiers (the ones silk-screened on the board are often obscured by the components), and draw them in on both the mylar and the schematic. Makes it real easy go from the schematic back to the circuit board.

Mark's Approach to Finding Information

Take the lowly 2N3055 power transistor, for example.... (Most of us have its specs engraved on some radiation-hardened neurons safely tucked away in a forgotten part of our brains but for the freshly minted EE or technician....

(From: Mark Zenier (mzenier@netcom.com).)

Places to look:

The web, at sites for companies that make power transistors. A whole bunch of people make jelly bean transistors like 2N3055s, down to some little 50 employee companies that you've never heard of, but they may not have a web site yet). Or start with one of the web directories. (Check the "Electronic Components" sections of Sam's Neat, Nifty, and Handy Bookmarks.)

The sales rep, sales office, or company literature department. Look in the phone book or on the web page for the phone number of a company or their local or regional sale representative or office. Call them up and ask. It's their job to provide customer support and if you sound like you halfway know what you're doing (saying you're a student works, too) AND it doesn't cost them much (don't get greedy) they'll often be more than willing to send you information. (These days, it might be a CD-ROM of their whole product line. Cheap, but not that easy to use, IMHO.) If they won't help you, ask them where there is someone who can. Like the nearest distributor.

Electronics distributors. Larger ones often fill the same literature distribution role as the sales rep. Other distributors like Jameco, JDR Microdevices, Future Active sell databooks as a catalog item. Or a local distributor that caters to the walk in trade will have a databook shelf and allow (or have a nominal fee for) photocopies. (The big distributors are closed operations, mostly using phone salesmen and UPS for distribution, visitors aren't necessarily welcome.)

A good library. Like one at a university with an electrical engineering program, or a large city library.

Used book stores, a big unselective 'book dump' often will have a good stock of old databooks. Ones that you can't get from the manufacturer and more. Likewise, electronics surplus stores (most big cities should still have one or two) often have them.

Parts Information and Cross References

Also see the section: House Numbers.

Here is the current Web site for NTE:

• NTE (NTE Electronics, Inc)

(From: Gregg (gregglns@ix.netcom.com).)

"NTE's device numbers are the same as ECG's, and their cross-ref guide can be downloaded from http://www.nteinc.com/.

It's free but they do want you to register. If you want to bypass this, go to ftp://nteinc.com/pub/ and download the windows version of the guide, ntesetup.exe. Don't bother with the dos version; the file named dosdisk2.exe is bad, and won't unzip."

I am not necessarily recommending using NTE (or other generic) replacements if the original replacements are (1) readily available and (2) reasonably priced. (Note that very often the original replacement part will be less expensive than the equivalent from NTE. Therefore, it should be used if available.) However, the cross reference can save countless hours searching through databooks, seaching the Web, or contacting the manufacturers. Even if you have a wall of databooks, this source is invaluable. However, there are a couple of caveats:

1. Some crosses have been known to be incorrect - the specifications of the generic replacement part were inferior to the original or totally wrong with different pinout or even function!

2. Don't assume that the specifications provided for the generic part are identical to the original. Since a single NTE part may replace multiple standard parts, it may actually be better in some ways. Thus, using one of these cross references to determine the specifications of the parts in your junk bin can be risky.

I often use the replacement guide to determine upper bound specs but as noted above, rarely buy any generic parts (sorry NTE). Then I find industry standard parts that have equal or better specs. Dalbani's catalog (see the section: Mail Order Parts Sources) has a sort of inverse cross-reference from NTE to 2S/2N/BU/whatever that isn't a bad starting point (though probably not to be trusted without confirmation of actual specs). Of course, this doesn't necessarily help with some tricky HOTs and choppers....

Note that while Howard Sams of Sams' Photofact fame publishes a semiconductor cross reference manual (or used to), it would appear to just be a compilation of the ECG, NTE, SK, and Radio Shack manuals - and much more expensive ($25 or so).

For standard ICs, IC Master used to be the "bible" for IC references. It can often provide quick access to complete data. Full access to their Web site is currently free but they do require registration. However, with their print version, ICs no longer manufactured were not listed. I assume the on-line version will be similar. Thus, it may be of only limited value for older equipment.

DigChip is one of a growing number of on-line services that provide cross reference and manufacturer links. Many like this one are free but require simple registration.

Transistor Designations

• U.S. made semiconductors used to be mostly of the 'nN' variety - 2N with a 3 or 4 digit number for bipolar transistor, for example. This is called the Joint Electron Device Engineering Council (JEDEC) standard numbering but seems to have been replaced by letter prefixes which may be manufacturer dependent although the same part may be available from multiple sources. These numbers are becoming less common and are rare in consumer electronics.
  • 1N: diodes.
  • 2N, 3N: bipolar transistors.
  • 4N, 5N: optocouplers.

• Many devices in consumer electronic equipment are marked with a letter (A, B, C, D, F, J, K) and a 3 or 4 digit number. Add a '2S' in front of this and the result is likely to be the complete (Japanese) part number (the '2S' is nearly always absent from the package label). You can often use this number to find a suitable cross from NTE. However, most of the common '2S' devices are available from places like MCM Electronics and Dalbani.
  • 2SA, 2SB: PNP bipolar.
  • 2SC, 2SD: NPN bipolar.
  • 2SF: thyristor.
  • 2SJ, 2SK: FET/MOSFET.

  There are many other '2S' prefixes but these are by far the most common.

  Suffixes may denote package type or some special feature like an internal damper diode (D, for horizontal output deflection transistors), enhanced gain, special speed sort, etc.

  A cross reference of sorts is availabe at Transistors Japonais (French). Don't worry, the device numbers are the same in French and English. :)

• Less common are designations which look similar to the Japanese 2S numbers (a capital letter followed by a 3 or 4 digit number and optional suffix) but are actually Korean part numbers to which you add a 'KT' (Korean Transistor or Type?) instead of a '2S'. So D998 becomes KTD998. These components typically have a capital 'K' on top in addition to the part number starting with the letter (e.g., A,B,C,D). However, sometimes the only way you will know is that ordering the 2S version gets you a device that isn't even close (like a tiny TO92 small signal transistor rather than the 200 W, TO3 type you expected)!

  There may be other examples but these are the exceptions (at least for now).

• Note that some components (usually ICs) may be labeled in a similar manner (like C4558C which is actually a dual op-amp) but this IS the complete part number - just something else to confuse you! Some of these such as one labeled C1003 may actually be a uPC1003 so if what you find in a datasheet doesn't make sense, try these other possibilities!

More on Transistor Designations

• II denotes the current rating in amps.
• T will be either N for N-channel or P for P-channel.
• VV denotes the D-S voltage rating in V/10.

(From: Mark Robinson (mark-r@snow_white.ee.man.ac.uk).)

We are lucky with transistors that, apart from a few oddities which I'll talk about later, most markings follow one of these codes. ICs are more tricky as you're often dealing with custom chips or mask programmed devices with manufacturers individual codes. A quick hint though: always look for known numbers (e.g., 723, 6502, 2764) etc. between the suffix and prefix, and beware of the date code.

Right... Back to transistors. The three standard transistor marking schemes are:

1. Joint Electron Device Engineering Council (JEDEC).

   These take the form:

   Digit, letter, serial number, [suffix]

   where the letter is always 'N'.

   The first digit is one less than the number of legs, (2 for transistors unless they're crippled although I'm not sure about 4 legged transistors maybe they get a 3) except for 4N and 5N which are reserved for optocouplers.

   The serial number runs from 100 to 9999 and tell nothing about the transistor except its approximate time of introduction.

   The (optional) suffix indicates the gain (hfe) group of the device:

   A = low gain
   B = medium gain
   C = high gain
   No suffix = ungrouped (any gain)
   

   See the data sheet for the actual gain spread and groupings. The reason for gain grouping is that the low gain devices are fractionally cheaper than the high gain devices, resulting in savings for high volume users.

   Examples: 2N3819, 2N2221A, 2N904.

2. Japanese Industrial Standard (JIS).

   These take the form:

   Digit, two letters, serial number, [suffix]

   Again, the digit is one less than the number of legs.

   The letters indicate the application area and flavour of the device according to the following code:

   SA: PNP HF transistor
   SB: PNP AF transistor
   SC: NPN HF transistor
   SD: NPN AF transistor
   SE: Diodes
   SF: Thyristors
   SG: Gunn devices
   SH: Unijunction transistor
   SJ: P-channel FET/MOSFET
   SK: N-channel FET/MOSFET
   SM: Triac
   SQ: LED
   SR: Rectifier
   SS: Signal diodes
   ST: Avalanche diodes
   SV: Varicaps
   SZ: Zener diodes
   

   The serial number runs from 10 to 9999.

   The (optional) suffix indicates that the type is approved for use by various Japanese organizations.

   NOTE. since the code for transistors always begins with 2S, it is sometimes (more often than not is seems) omitted so, for example, a 2SC733 would be marked C733.

   Examples: 2SA1187, 2SB646, 2SC733.

3. Pro-Electron.

   These take the form:

   Two letters, [letter], serial number, [suffix]

   The first letter indicates the material:

   A = Ge
   B = Si
   C = GaAs
   R = compound materials
   

   Needless to say the biggest majority of transistors begin with a B.

   The second letter indicates the device application:

   A: Diode RF
   B: Variac
   C: Transistor, AF, small signal
   D: Transistor, AF, power
   E: Tunnel diode
   F: transistor, HF, small signal
   K: Hall effect device
   L: Transistor, HF, power
   N: Optocoupler
   P: Radiation sensitive device
   Q: Radiation producing device
   R: Thyristor, Low power
   T: Thyristor, Power
   U: Transistor, power, switching
   Y: Rectifier
   Z: Zener, or voltage regulator diode
   

   The third letter indicates that the device is intended for industrial or professional rather than commercial applications. It is usually a W,X,Y or Z.

   The serial number runs from 100-9999.

   The suffix indicates the gain grouping, as for JEDEC.

   Examples: BC108A, BAW68, BF239, BFY51.

   Apart from JEDEC, JIS and Pro-electron, manufacturers often introduce their own types, for commercial reasons (ie to get their name into the code) or to emphasize that the range belongs to a specialist application.

   Some common brand specific prefixes are:

   MJ: Motorola power, metal case
   MJE: Motorola power, plastic case
   MPS: Motorola low power, plastic case
   MRF: Motorola HF, VHF and microwave transistor
   RCA: RCA
   RCS: RCS
   TIP: Texas Instruments power transistor (plastic case)
   TIPL: TI planar power transistor
   TIS: TI small signal transistor (plastic case)
   ZT: Ferranti
   ZTX: Ferranti
   

   Examples: ZTX302, TIP31A, MJE3055, TIS43.

   Many manufacturers also make custom parts for large volume OEM use. These parts are optimized for use in a given part of a given circuit. They usually just have a manufacturers stamp and an untraceable number. Often when a company goes bankrupt, or has surplus at the end of a production run, these transistors find their way into hobbyist bargain packs. There is no way that you can trace data on these devices, so they are only suitable as LED drivers, buffers, etc, where the actual parameters are not important. Check carefully before buying.

Once you have identified your part, a trip to the data sheet or equivalents book is called for (anyone know of an on-line equivalents list?).

Surface Mount Parts

• Resistors are often labeled with 3 or 4 itty-bitty digits where the last one is the multiplier (10 to the Nth power).

• Capacitors are often totally unlabeled but larger electrolytics may have both capacitance and voltage rating. Non-electrolytic types often have a brown body. Electrolytics may be black, yellow (tantalum), or some other color.

• Discrete semiconductors can often be identified by the number of pins using an ohmmeter at least in a rough sort of way. However, the only way to determine their specifications (and often even the type) or to find a cross reference for the abbreviated markings like 1A, B2, 2J, is to look them up since there is no logical relationship between the marking and the actual part number (unlike the 2S discrete parts, for example). This can be done if you have the manufacturers databooks or possibly even their abbreviated catalog (e.g., Motorola's "Master Semiconductor Selection Guide". NTE does cross a few of these SMT parts but their coverage is not nearly as comprehensive as for normal (through-hole) counterparts.

  The Web sites of semiconductor manufacturers may also have some information but this varies widely from company to company.

  An on-line list can be found via the S.E.R FAQ Main Table of Contents (near the bottom).

  This is also somewhat incomplete. And, several other very nice ones at:

  • Rob's Electronics Site SMD Marking Codes
  • Technical Knowledge Base for You: SMD Marking Codes
  • SMD Codes (German Web Site 1)
  • SMD Codes (German Web Site 2)

• ICs. The only option for many of these is to locate the databook or Web site with the datasheet. Even if the part number is similar to a through-hole version, the pinout may differ. However, common TTL/logic chips and op-amps will usually have identical pinouts and specifications. It is often possible to partially confirm this by checking the location of the power pins or known signal connections.

House Numbers

Are house numbers used just to make life difficult?

It certainly seems that way from the perspective of repair. Give me industry standard numbers anyday. However, house numbers are a fact of life.

The house number is what you need to order a replacement from the original manufacturer of the equipment but that may not always be desirable due to the likely high cost and possible difficulty in locating a suitable distributor that carries the manufacturer's replacement parts.

As noted in the section: "Parts information and cross references", a Master Selection Guide like NTE may be able to give you some idea of the specifications even if you don't want to use their generic replacement semiconductors. Their web sites have (or should have in the future) some amount of cross reference information for industry standard and house numbers. However, don't expect to detailed IC specifications or even pinouts in most cases there or from the disks they may also offer. The hard-copy Master Selection Guides which these companies sell have been better in the past (though this may be changing) but even these won't give you all the details. However, if you do repair work regularly, these 'telephone book' thickness guides worth the few bucks that is charged.

Also see the section: Parts Information and Cross References.

Generic Parts (Mostly Semiconductors)

Other common components including flyback transformers, belts and other rubber parts, and RF modulators may also be available from these sources but they tend to be used less often and quality may vary even more.

There are some other similar companies like SK (part of Thomson Consumer Electronics) but NTE now appears to dominate the industry for these generic replacement semiconductor and other electronics components.

HP-to-Industry Standard Semiconductor Cross Reference

Sphere's Used Electronic Test Equipments will help decode all those odd 1820-xxx numbers! Also HP and Tek repair parts and equipment on line, plus helpful FAQs and links to all kinds of test gear sites.

We also have a big used equipment site on line for Canadians.

Internet Sources of Information

Tandy (Radio Shack) used to have a nice web resource and fax-back service. This was mostly for their equipment but some of it applied to other brands and there were diagrams that were useful for other manufacturers' VCRs, TVs, CD players, camcorders, remote controls, and other devices. However, the page is long gone and no realy useful info is obvious on Tandy's Web site.

Are There Schematics of Consumer Electronic Equipment on the Web?

You are searching for the Holy Grail. Everyone is, but it isn't going to happen on a large scale - at least not for free. Schematics are copyrighted by the equipment manufacturers who sell them as part of their service manuals or license them to organizations like Sams Technical Publishing (Sams' Photofacts) and others.

• If you reverse engineer - trace - the schematic of a piece of equipment from the unit itself - and can prove it - and then make it available at your Web site, that is probably legal. You'll have a hard time proving it though for something like a TV or VCR.

• However, if you scan a service manual or Sams' Photofact and make that available at your web site, you may eventually find yourself in court. For schematics from original service literature of obsolete equipment, the chances of the manufacturer wanting to spend a lot of money on lawyers is small but for newer equipment, they may indeed - or just to make an example at your expense. A scanned Photofact is likely to be a problem regardless of age.

That is my take, at least.

Having said that, there are many Web sites with schematics that may or may not have been legally copied and made publicly available. See the section: Additional Sources for Service Information and Manuals.

Taking the Unit to a Repair Shop

To paraphrase a famous quote: 'The only stupid or useless information is that which is not provided'. However, unless you really are sure of what you are talking about, don't try to tell the repair person what you think the problem is likely to be. Don't bombard them with technobabble full of buzzwords - any competent tech will see right through that. You can be sure that if you mention that you suspect the expensive flyback is toast, it will be diagnosed as bad. Let them do their job. Listen carefully to their diagnosis. You should be able to tell if it makes sense.

Searching for Information from USENET Newsgroups

There is an excellent chance that your question has come up and resulted in information being passed back and forth on sci.electronics.repair (or other appropriate newsgroup). For example, if you have had problems with a late model RCA/GE television, there have been dozens if not hundreds of postings on this subject over the last couple of years. There is no need to add to the clutter.

Google Groups (formerly Deja.com/DejaNews) includes a USENET newsgroup searching facility. It has been archiving newsgroup articles since March, 1995. By going to their web site, you can invoke a search of over 45,000 newsgroups (hundreds of GB of data!) for any set of words, names, or email addresses. Within *seconds*, they will provide a list of postings that satisfy your search criteria. Try using Google Groups at least once - you will be instantly hooked. :( Some of the relevant site URLs are:

• Google Groups Homepage
• Usenet Advanced Search

• Articles on Sci.Electronics.Repair

While postings typically drop off of your local server in a few days or less, Googlegroups maintains them *forever* so that locating an entire thread becomes a trivial exercise in identifying a search string that will narrow down the postings to those relevant to your needs.

There are many other services available via Google Groups including newsgroup posting (under constructio apparently during the transition from Deja.com).

Speaking of posting:

Posting to the Sci.Electronics.Repair Newsgroup

Even if your ISP doesn't provide USENET newsgroups or allow posting for some reason, you can always access them (read, search, and post) via Google Groups. See the section: Searching for Information from USENET Newsgroups.

No matter how you do it, however, here are some tips that will get you what you want without unnecessary flame wars:

• Please read the on-line repair FAQs or repair guides first. Your problem may be covered. Even if an exact solution is not provided there, the additional information may allow you to ask your questions more concisely and intelligently and therefore arrive at a solution more quickly.

  The FAQs can be found at:

  • Sci.Electronics.Repair FAQ (RepairFAQ.org)

  and its mirror sites. First read the README and Mirrors links to identify the best way for you to access the information from your location.

• Put the type of device (i.e., VCR, CD player), manufacturer, and model number in the subject header as this will get the attention of the professionals. If you do not provide this info, the first reply you will receive will be to provide it. Avoid this waste of Net bandwidth. For general questions, such info may be unnecessary, but it will not hurt.

• As with professional repairs, provide as much relevant information as possible. Ambiguity can lead to totally bogus advice. For part identification, include both the designator (e.g., R324, Q1) and type (e.g., 330K, BU407D) if available.

• Don't just ask for repair tips - describe in chronological order what you have done so far in terms of troubleshooting approach and tests performed but don't fill screen upon screen with details. People don't want to read a lot of filler. Include only the essentials.

• Turn off any fancy formatting like HTML or WORD! Use plain ASCII text since everyone can read that, formatting adds NOTHING to the content, takes up space, and is very confusing for those people whose news readers cannot interpret it.

• Take a bit of time to make sure what you have typed is legible. Spell checking it won't hurt. DO NOT use ALL CAPS - that is like shouting in cyberspace and a good way to be ignored.

• A bit of courtesy won't hurt as well. Many people who reply won't care about the use of please, thank you, and any help much appreciated, but none of these will hurt and don't take much effort.

• If a little circuit diagram will help, provide it in ASCII if possible. ASCII takes up almost no space and everyone (with a fixed width font) can read it. Here are some basic guidelines for creating legible ASCII schematics:
  1. Use a fixed-width font like Courier, Lucida Console, Quick Type Mono, etc.

  2. Make sure your line length is set to 78 characters or less.

  3. Use SPACES rather than TABs - TABs interpret differently depending on terminal or newsreader settings and the alignment gets messed up when text is included in a news posting.

  For numerous examples of ASCII schematics that should look fine, see: Various Schematics and Diagrams.

  Large binary files are not supposed to be posted on these newsgroups. In addition, you will upset people who are forced to download a 1 MB file they have no interest in but may not know it until they see the description. Some ISPs charge for connect time and bits transferred. If you have a large scanned schematic and you think it really will help with a diagnosis of or solution to your problem, offer it via email, upload it to your Web site, or post it to the newsgroup: alt.binaries.schematics.electronic (but not all news servers carry this group).

• You need to be patient. Not everyone sits at their computers all day. Some news servers may be days behind in their postings. If you truly get no replies of any kind (to the newsgroup or email) in a few days, repost your question with a note that it is a repeat. The net isn't perfect and due to finite disk space, many servers will miss postings or purge them after a day or less. Sometimes, your posting may not have made it out of the bowels of your computer system. You should be able to check this via - see below.

• Don't ask for help on 25 problems in the same posting - that is taking advantage of the generosity and time of others. Dribble them out and reciprocate by replying to other people's problems as well if you can but not to just say something. If you act immature, you will end up in everyone's kill file.

• Don't ask for help on problems that you could just as easily solve on your own by checking a databook you should have or a Web site that you should know about.

• Don't ask for an email response. First of all, it is very impolite. Sci.electronics.repair was not created for your benefit. We do this because we like to help people but at the same time do not want to feel like we are being taken advantage of or taken for granted. We are not your private consulting service. In addition, others will know when an adequate response to your query has been provided and will not need to waste their time repeating the same information. And, everyone will learn something in the process.

  More importantly for you, receiving replies via email will circumvent one of the most important functions of the newsgroup - cross-checking to locate errors in responses either because the responder didn't know what they were talking about or made an error in interpretation. Perhaps, they were just being a bozo and sent a totally bogus or even dangerous response. And, some people may have hidden agendas that aren't in your best interests. If that was the only reply, you would never know. While there is a lot of high quality information available via the Internet, there is also a lot of noise. Yes, you will need to read the newsgroup for a few days. That will be a small sacrifice and well worth the effort.

  If your news feed is indeed poor - as many are - and you are honestly afraid of missing the responses, then phrase your request for an email reply in such a way that it doesn't sound like you are totally immature and lazy.

  Another alternative is to search for replies at:

  • Google Groups (formerly Deja.com/Dejanews.)

  This service will enable you to search for only the postings you are interested in and seems to be pretty reliable. They subscribe to a half dozen news feeds just to avoid missing *your* postings!

  Many people will send you a CC of their posting anyhow so avoid getting flamed for poor netiquette. However, take note below.

• Use your true full name and email address in the 'Reply-to' field of your posting. It is unreasonable to expect us to reformat a bogus email address that you might use to avoid SPAM. It is quite annoying to try to help people only to receive bounced mail. While the 'delete' key works quite well in dumping the returned message, you don't get your questions answered. The regulars on the sci.electronics.xxx newsgroup hierarchy all use their real names and email addresses. Please do us a favor by being mature and do the same. Spammers lurking around these sci newsgroups get pummeled anyhow and don't survive for long. :-)

• Don't accept the first response as the definitive word. Gather a few replies and followups and then you will be able to make an evaluation of which to believe and act upon. Post a question for clarification, if needed.

• If you do receive email responses, reply to the senders as well as posting to the newsgroup *and* indicate to the senders that you are posting a copy to the newsgroup.

  It is very annoying to reply via email only to find that the same question appears a little later on the newsgroup requiring a repeat response.

  In any case, once your problem has been resolved (or you have given up), it is polite to post a concise summary of the problem, suggestions, the solution or frustration, and appreciation to those who have helped you.

Private Discussion Groups and Email Listservers

There are also a few repair related email listservers. These require that you subscribe by sending a special email message and/or filling out a form. Some may have merit in that experts are more likely to be subscribers and they are forced to at least receive all emails (even the next stop is the bit bucket!).

Sorry, given the relatively low interest in both private discussion groups and email listservers, I can't justify attempting to keep up with their arrivals and departures! :) Both of these can be found through the various tech-tips sites as well as by searching postings on the Sci.Electronics.Repair Newsgroup via Google Groups Advanced Search. A few may also be listed in my Bookmark File.

Having said that, popular services like Yahoo often host at least a few niche discussion groups that simply due to the number of users, have a volume of traffic worth noting. For example, go to Yahoo Groups and search for "Tektronix". Two groups for Tektronix oscilloscopes will pop up, one for general postings and the other for documentation like schematics.

There are also some like Fixya.com that aren't generally very technical but may be of use in finding answers to common product-specific repair problems.

Dealing with a Repair Shop in an Efficient and Professional manner

(From: Rex (bopeep@prysm.net).)

I have been asked to give tips for dealing with repair shops. It is sometimes difficult for the average consumer to convey their needs to shops or technicians.

• Limit the scope of the problem to the actual problem you are having with your product.

  Avoid getting into dialog about children, grandchildren, holidays, bad mouthing other shops or manufactures, "I can get a new one for that", vacations, school functions, how seldom you have used the product or anything that that has nothing to do with you product's failure.

• Ask for an ESTIMATE, but realize that an ESTIMATE can and MAY be raised or lowered. You MUST be advised of any change to the estimate before you are billed for a unapproved amount.

• Avoid GUILT, RUSH (unless you are willing to pay for it), and pressure to the shop. Be polite and EXPECT to be treated politely and you should be given the respect that any business should give their customers.

• If the repair does not meet your standards:
  • Ask for and expect, that something will be done as quickly as possible.

  • If the shop fails in its obligation to you, call the BBB, consumer affairs agencies or any other place that can help you resolve the problem if the shop refuses to honor its warranty.

    CAUTION: Be VERY sure what the warranty is. Most repairs are covered for the work done, not the entire operation of the product. Read the shop warranty and ASK questions.

  • Do NOT expect a shop to clean up or repair problems from other repair attempts (including your own), or to be able to repair a product that has be abused.

Parts Sources

Where to Go for Parts

However, none of these places have even the most basic service parts for consumer electronic equipment. You won't find a single rubber belt, RF modulator, posistor, or video head, nor most Japanese semiconductors within their thick catalogs.

It may be possible to go direct to the manufacturer of the equipment but expect to spend many times the true price of a part to get it from the horses mouth. In most cases, a totally identical part - with the manufacturer's logo and everything - meeting identical specifications is available elsewhere at a fraction of this cost.

Web Parts Information and Ordering

• Panasonic Parts & Service Online

Mail Order Parts Sources

And, Don't Forget Radio Shack

In addition, Tandy, the parent company of Radio Shack is worldwide and may actually offer a USEFUL selection of components:

(From Ted Gondert (vcrepair@bbs.industrynet.net).)

Tandy (aka Radio Shack) has a new catalog available at your local Radio Shack; "Tech America" "Your Electronics Resource". This is special mail order catalog with many parts available from a different division of Tandy. There is no minimum order and parts are sent directly to your house. Shipping is $4.00 for components orders only or various rates up to $13 for orders of $500.

Call 1-800-877-0072 between 7 a.m. to 11 p.m. M-F Central Time, 9 a.m. to 8 p.m. Saturday, 11 a.m. to 7 p.m. Sunday. Fax 1 800 813-0087. Mail: Tech America, PO BOX 1981 Fort Worth, Texas 76101-1981.

This catalog, Sept 1997 has 546 pages with capacitors, resistors, transistors, IC, coils, wires, antennas, test equipment, tools, radios, security equipment, books, etc.

The capacitors include high temperature, 105C electrolytics. The integrated circuits and transistors are mostly American type part numbers, digital, op-amps, etc. not the Japanese type used in most consumer electronics today. But should be many parts that electronics techs can use.

For example; 1000ufd 16 volt 105C electrolytic capacitor is only 39 cents. (pg 14) That's popular size in use in Panasonic SMPS. Also has MJ15024 audio output transistor for $4.59 (pg 49) and surface mount transistors.

Radio Shack also has catalogs in stores for RSU, Radio Shack Unlimited. Those show Japanese semiconductors, special batteries, phono stylus, equipment, etc. that your local Radio Shack can order.

(I haven't ordered anything yet but after checking my inventory and budget will probably stock up on some capacitors, etc. Get most of my parts from MCM, MAT Electronics, etc and some local distributors.)

Troubleshooting of Intermittent Problems

• A computer monitor that erratically loses one of its primary colors (red, green, or blue).

• TV reception that turns to slow and then returns to normal apparently at random. Or one that turns itself on at maximum volume in the middle of the night.

• A car radio or tape deck that misbehaves on rough roads.

• A TV that turns itself on in the middle of the night.

• A CD player that is prone to aborting or skipping at random times

• A microwave oven that blows its main fuse once in 10 days.

• A TV that exhibits annoying herringbone patterns at certain times of day.

TV and Monitor Manufacturing Quality and Cold Solder Joints

Any intermittent problems with monitors that cause random sudden changes in the picture brightness, color, size, or position are often a result of bad connections. Strategically placed bad connections can also cause parts to blow. For example, a bad connection to the SCR anode in a phase controlled power supply can result in all the current passing through the startup resistor, blowing it as well as other components. I had a TV like this - the real problem was a bad solder joint at a pin on the flyback. Thus, erratic problems, especially where they are power or deflection related, should not be ignored!

Bad solder joints are very common in TVs and monitors due both to poor quality manufacturing as well as to deterioration of the solder bond after numerous thermal cycles and components running at high temperature. Without knowing anything about the circuitry, it is usually possible to cure these problems by locating all bad solder connections and cleaning and reseating internal connectors. The term 'cold solder joint' strictly refers to a solder connection that was either not heated enough during manufacturing, was cooled too quickly, or where part pins were moved before the solder had a chance to solidify. A similar situation can develop over time with thermal cycling where parts are not properly fastened and are essentially being held in by the solder alone. Both situations are most common with the pins of large components like transformers, power transistors and power resistors, and large connectors. The pins of the components have a large thermal mass and may not get hot enough during manufacturing. Also, they are relatively massive and may flex the connection due to vibration or thermal expansion and contraction.

Why Can't TV Manufacturers Learn to Solder Properly?

1. Mass of large component leads (like shields) does not get adequately heated during manufacture leading to latent cold solder joints. While they may look OK, the solder never actually 'wetted' the heavy pins and therefore did not form a good mechanical or electrical bond.

2. Thermal cycles and differential thermal coefficients of circuit boards, traces, and solder. While it is not easy to do anything about the material properties, using plated through-holes or a similar mechanical via would greatly increase the surface area of the joint and prevent the formation of cracks.

3. Vibration. This is also directly related to the single sided circuit boards without plated through-holes to strengthen the joints.

4. Lack of adequate mechanical support (single sided circuit boards without plated through-holes (vias).

The Sony and RCA/GE tuner shield problem is interesting because this could have been solved years ago at essentially no additional cost as other manufacturers - and their own repair procedures - have proven.

Attacking intermittents

The most common external causes would be electro-magnetic interference, either through the air or via the power line. For more on these in particalur, see information on interference in the documents on TV and monitor repair. But, suffice it to say, changing the location or electrical power source will usually help to narrow it down.

If internal, it may be physical, heat related, or mode related. Gentle whacking (yes, whacking is an acceptable diagnostic technique but don't go for the 12 pound hammer!), pressing, flexing, cable wiggling, etc., can and should be used in an attempt to confirm at least that there is a physical cause inside the unit. Doing these tests just as the problem comes or goes is the best time as whatever is marginal, will be most marginal then.

If the problem appears or disappears, or does both, over a period of time after the equipment is turned on, then temperature is almost certainly a factor as the circuit board and components expand.

The most common physical problems are bad (cold) solder joints, connectors that need to be cleaned and reseated, and bad cables or cable connections. Perhaps surprisingly, though components may fail internally and result in erratic behavior, this is probably lower on the list of likely causes than those listed above. Some exceptions would be mechanical relays in audio power amplifiers, phone equipment, and elsewhere; hybrid power amplifiers, and other power devices.

The whacking, etc., can be done without taking the cover off the equipment and may or may not reveal anything. In either case, you will have to go inside. But if there is an effect, then you will know that the problem IS inside and further tests will need to be done to identify the specific cause.

Once the cover is off, there still may be quite a challenge to find the specific solder connection or contact that needs attention. Knowing something about how the actual circuit area relates to the symptoms will help narrow it down. For example, if there is a loss of vertical deflection in a TV or computer monitor, the most likely areas to attack will be the vertical deflection output stage and its power supply feed.

For popular consumer electronic equipment, intermittent problems are often present in many (or even most) samples of a particular model over the course of its life. Therefore, checking a tech-tips database or asking on the USENET newsgroup sci.electronics.repair may reveal a common cause and an easy solution ("resolder the flyback pins"). There are a list of tech-tips databases at my Web site, www.repairfaq.org.

(From: Phil Buble N1GTZ (muttnik@ecr.net).)

A note on whacking as a troubleshooting technique, at home and in the shop.

I'm not what you would call a full time electronic repairman though I have made a living doing it commercially. I can be just helping a friend out at home but usually it's been an adjunct to my main work as assembler/post flow touch-up and I'm pretty good at it. Therefore most of my repair experience is with new equipment that doesn't work correctly the very first time it's powered on. (and yes when *will* that wave-solder machine learn to solder? :) Running that thing is a art-form I'm glad to avoid)

Naturally in such a situation I'm a great believer in "swap-out with NGP testing" since there's usually lots of them in an assembly shop but this cannot always be easily done. Especially at home, with obsolete units or those so small or cheaply made not a vacuum tube, IC or module is to be found in a socket. My funniest experiences with whacking regard these - one commercially and one at home. The commercial one first:

It involved a totally obsolete and smallish sensor board used in the ground-water monitoring industry to measure water pH deep down in wells. Even carefully sealed you can imagine the condition it was in after years of hard use. Only a few had ever been made by the company long before and the engineer who designed it equally long gone. A young, recently hired engineer was given the task of finding out what was wrong. It was giving rather useless and erratic readings and needed to be repaired in a hurry. I cleaned it and reflowed all joints, just in case, then turned it over to him since it still didn't work. After hours of frustration and attempts to get "into the head of the designer" he gave up and I asked to give it a try. By then I had a hunch. I made a routine test to make sure all was getting power - then gave the PCB a whack and a little twisting action. It began working perfectly as long as the PCB had a slight twist to the right. This literally took me all of about 5 minutes. You have never seen such a dumb-founded engineer! They do need to get out more! Even with the failure mode detected the cracked trace could not be found in a reasonable time so I had the honor of transferring all the parts to a new PCB. Amazing they even had one.

The second funny situation occurred many years before the above and happened at home. A neighbor brought over a old (even for the time) but nice condition 19" tube-type B/W TV hoping I could fix it. Fully half this set was point-to-point wiring, no PCBs at all. I'm old enough to have one foot in the all tube and "condenser" era and one foot in the transistorized world so it didn't matter to me that it was tubes. As long as my friends are willing to pay for the parts and hopefully locate a schematic I'm willing to at least try. It's all done in a casual sort of way. (Side note: You'll have to pry my Heathkit AA-100 Vacuum Tube Stereo Amp from my cold dead hands, it still sounds great 41 years after it was built)

This one located the Sam's Photofacts for it, complete with schematic and pin voltages. A resistor in the B+ line to the plate of the Horizontal output tube had burned out. That was replaced and all DC pin voltages then looked OK - yet no picture. Sure, the H Oscillator wasn't oscillating! The next logical thing to do was to swap-out the H output tube with another to see what happened. I told my neighbor we needed to locate a tube, and a rather expensive one, to go any further. He didn't bother, it wasn't worth the effort or expense. 5 *YEARS* later he trots out that same TV hoping, once again, I could get it to work. I tell him we still needed that tube. He shrugs, plugs it in, turns it on and gives it a good whack. It came on and worked perfectly! That's all it needed all along, my power-supply repair had fixed it 5 years before but no one ever whacked it to get it started again.

Selective circuit whacking's been one of my most productive and time saving

Inspection and Power Off Tests for Intermittents

• Start with the pins on devices like power transistors, transformers, and large or high current connectors. These are most likely to cause marginal solder connections to break apart due to thermal and physical stress. Hairline cracks at solder joints is a primary cause of intermittents, especially in TVs and monitors with their power supply, deflection, and video circuitry that may run hot.

  Make the inspection under a bright light. If your closeup vision isn't perfect, use a good magnifier - these may literally be hairline cracks and their visibility may be obscured by reflections from the solder joint. Use a pointed stick (not something metal if possible) to gently prod any suspicious looking pins to see if they move. Look for discolored patches on the circuit board. Such discoloration isn't in itself a problem unless it is severe but indicates that hot components live there or nearby and bad solder joints are very likely.

• Check for tan or brown glue on the top and bottom of the circuit boards. A rigid adhesive may be used to attach various components but some varieties decompose and become conductive with heat and age. Some very weird problems have been linked to decayed glue! So, carefully scraping it away and replacing it with non-acidic RTV Silicone or similar adhesive may be prudent. However, I don't know how to tell which types are a problem.

• Check for loose or damaged cables (particularly in user serviced equipment like PCs!).

• Remove, inspect, clean (if necessary), and reseat all internal connectors. Even if they don't seem to be in an area of the circuitry that is relevant, they could be feeding a power or control signal. Check for discolored or fatigued contacts as well as physical damage to the wires and improperly made crimps. If any components (like transistors or SIMM memory modules) plug in, do the same for them.

• If a suspicious area is located, it may be possible to use an ohmmeter between selected pins to determine if a connection is intermittent. To increase the chance of detecting a momentary change in resistance that may be too brief to register on a meter, connect the input of an amplified speaker (or audio amp and speaker) in parallel with the meter probes.

Power On Tests for Intermittents

• Using an insulated stick, start gently prodding likely areas of the circuitry in an attempt to make the problem come and go. If you are successful, don't assume the journey is over! Pressing at a corner of the board may have an effect at the opposite side. In fact, you may find that pressing *anywhere* appears to have about the same effect. It may take some vary very light tapping, flexing, etc., to locate the culprit. Until a physical cause if actually located (e.g., a visibly cracked solder joint where the pin can be see to move!), don't assume you're home free even if the problem appears to clear up. In fact, it is very common for an intermittent problem to go away as soon as troubleshooting begins not to reappear for several days or more - but it will reappear!

  Once a particularly sensitive area is located, use a stick thin enough to just touch a single pin at a time. Sometimes, a probe with a pointed metal tip, insulated for all but the last 1/16" or so, will be useful as it can get into the area between the pin and solder pad where cracks may have developed but are not visible. The metal tip will bridge the gap causing a change in behavior.

• If the cause is heat related, no amount of prodding (or cursing) may result in the problem occurring with the cover off. In this case, a heat gun (or blow dryer) may be needed to carefully warm up selected areas of the circuitry in an effort to identify the culprit. A blower with no heat may be used for cooling. Or, "circuit chiller" or "cold spray" may be used for more aggressive spot cooling. However, simply removing the cover may have altered something physical. For example, one of the cabinet screws may be to long and is shorting out something - this may be either from improper prior reassembly after repair or a manufacturing or design defect.

• The hardest intermittent problems to locate are those that occur infrequently and for only a short time with no chance of making a measurement. There are fancy and expensive recording analyzers for just such occasions (but you can buy a nice car for what one of these costs!). However, there may be no need for such extravagance. If you have an oscilloscope and camcorder or video camera/VCR, you probably have all that is needed.

  For a TV or monitor, point the camera at the CRT and the scope screen so that they are both in the picture and record on a 6 hour tape. Then, when your event takes place, you have a permanent record!

  That old video camera will be perfectly adequate. It doesn't need a 100X digitally stabilized enhanced reprocessed zoom or 1/10,000th second shutter. It doesn't even need to be color!

  Sure, this won't capture the 1 ns glitch. But, for the occasional flash in the picture, it is more than adequate to eliminate a video signal line as the source of the problem.

Now the question comes up: How can the re-occurrence of intermittents be prevented? For cracked solder joints, in addition to using proper soldering techniques for repair, it should be possible to add some "reinforcements" in the form of bare wire wrapped around the pin and extending out to the circuit board trace or even to an adjacent component pin. This will be better than just using more solder. For the CTC175 etc. cases discussed below, there is also special "elastic" solder that supposedly should be used. But, there are mixed reviews on whether this really helps.

Some equipment may also benefit from a small amount of additional cooling. A small fan can be added to draw air out of the cabinet. This will improve reliability since most components are happier being cool but will also reduce the extent of the thermal cycles reducing the likelihood of bad solder joints developing in the future.

RCA/GE/Proscan and Sony TVs

Some Sony TVs suffered from a similar set of bad solder joints, usually in the tuner or IF (metal) boxes. The most common location for the problem for many of these was to one pin of a coil inside the IF box which always seemed to lack adequate solder.

Much more information on the RCA/GE/Proscan and Sony solder problems and solutions, see the documents: RCA/GE TV CTC175-187+ Solder Connection and EEPROM Problems and Sony TV Tuner and IF Solder Connection Problems.

Other makes and models of TVs have similar problems with solder joints but not to the extent of these.

Perfecting Your Skills

Where to Find Equipment in Need of Repair or Abuse

• One obvious source are accomodating relatives, spouses, and collegues. However, again, you will want to hold off on this until you have some success under your belt.

• Garage, yard, driveway, porch, etc. sales (also tag and house sales but this may be higher class more expensive junk) can be veritable bonanzas of dead appliances. With a little restraint (don't buy the first items you see until you have a feel for what the going rates are) you should be able to buy excellent dead items for next to nothing. For example, I usually don't pay more than $5 for a dead VCR - maybe $10 for a late model in excellent physical condition. I bought a 26" RCA Colortrak TV for $5 and a late model 20" color TV for $3. CD players with problems typically go for $2 to $7. Sometimes they will just give you the stuff so they do not have to haul it to the dump. Much of this can be repaired inexpensively once you have some experience. If you mess up some of the patients, so be it. You will have learned a great deal and sacrificed little.

  Always check to see that you got all the accessories - remote controls, cables, attachments, etc. Often, they will have long since disappeared but it won't hurt to ask.

  Try to find out what the symptoms were from the owner if possible. With a little knowledge, this could improve your bargening position as well - or make you decide to try for a lesser challenge:

  "Jonny stuck a peanut-butter-and-jelly sandwich in the tape slot and when his pet hamster wen't to eat the sandwich it got stuck. They have both been there for a couple of years now. I put the VCR in this plastic bag to protect it from moisture. It really is a great VCR".

  or:

  "Well, there was this lightning strike, the modem exploded and 6 foot flames leaped out of the monitor so I dumped a pitcher of lemonade on it to put out the fire. What is left of the PC is still melted to the floor but I figured someone could use the monitor."

  I would skip those.

  Another high risk would be a piece of equipment that had been worked on by someone not competent to change a light bulb:

  "My VCR wouldn't play my Rambo tape so I opened it up and found this silver thing was out of line - you know, all cockeyed. So I tried to straighten it with a pair of Vise Grips(tm) but I must not have done it quite right as now all I get is snow and it makes these crunching noises. Maybe you will have more luck"

  or:

  "I tried to repair this amplifier but while I was making some adjustments, my screwdriver slipped and there were these HUGE sparks and bubbles appeared on several of those black things that look like cochroaches and parts flew off of those clips glued to this plate at the back. You wanted a challenge, right?"

  or:

  "Duh, I thought I would get cool music in my car but for some reason I cannot fathom, the jumper cables I used got really hot and my portable CD player now smells really bad and doesn't work on the normal transformer anymore. I will throw in the jumper cables for nothing."

  I would pass on these as well.

  In addition to melted or scorched cabinetry and the wonderful aroma of charred circuitry, look for the absense of cover screws and chisel or chainsaw marks!

• Moving sales are similar and better in some ways as the owners are usually very motivated to move out as much junk as possible.

• Flea markets may yield simliar types of items but expect to pay more. Where do you think they obtain all their merchandise?

• Thrift stores, Goodwill's, and similar outlets may also yield suitable candidates in some cases for free. Find out when their 'drop-off' days are and camp out. :)

• Auctions have potential as well but you better know even more about what you are bidding on, set a hard upper limit for you bids, and be prepared to spend the day.

  I like to swoop in and swoop out - thus my preference for garage sales.

• The curb, local dumpsters, and the town dump can also be sources but confirm that whatever you are taking is really up for grabs! One recommendation is to drive around a college campus at the end of the term when students are packing up and throwing away anything that they will not be taking home. There are even supposed to be USENET newsgroups on these topics. For example, alt.dumpster though I've not actually found it.

• Internet forums including those that specialize in buy, sell, and trade, as well as some specifically devoted to reuse of used stuff may produce more results than your house can accommodate. One example is Freecycle.org. But many other bulletin boards or newsgroups can be useful, particularly if they are reasonably local. Requesting a dead VCR from Outer Mongolia probably doesn't make sense unless you happen to live nearby. :) I've even had success asking for dead CD player optical pickups on sci.electronics.repair and now have a carton full of them. :) Haggling at garage sales may be more fun, the there's something to be said for the convenience of junk acquisition from the comfort of your computer chair.

  (Portions from: Iain E. Davis (feaelin@kemenel.org).)

  "Freecycle is actually a large group of mailing lists (theoretically, one for each city, township, or village) on the Planet) where people who have things that they'd normally just throw away, offer for "free (re)cycling" instead. Most of these lists will take "WANTED" posts as well. So a good technique is to post to a relevant list with something like: "WANTED: Broken consumer electronics" or in my area its wiser to say "WANTED: Broken VCRs, TVs, computers, etc.". I've actually acquired more stuff than I really know what to do with this way."

The most annoying situation is when after haggling over the price of a 'dead' VCR, you get it home with great expectations of the challenge ahead only to find that it works perfectly or your Mark-I thumb is all it takes to clean a supposedly trashed video head (but you do have to know the proper technique and incantations!) I ended up with a couple VCRs like that. A 'dead' CD player for $5 magically cured itself on the back of my 10 speed bicycle. Often problems are simple and easily remedied resulting in quick gratification. However, there will be real dogs which could more than make up for the easy fixes (like the GE TV with the never ending string of bad solder connections). At least, if you sell the easy ones, this will help pay for your 'habit'.

• Repair shops. They will literally have walls of beyond hope, dogs, or unclaimed equipment - TVs, VCRs, CD players, etc. It might be worth asking if you can buy some of these for a modest fee. While I am always tempted to save everything on the off chance that a part will be useful in the future, realiztically, this rarely turns out to be useful and they may be happy to part with what they consider junk especially if they have more than one of the same or similar model cluttering up their back wall.

  I do not know how viable an option this typically is since I have never tried it. (However, I used to trash pick mostly replaced vacuum tubes - nearly always tested good - back in those days when such things were common.) If they consider you a threat to their business, you may get the cold shoulder. If they consider you a future employee - or suspect you will make whatever you are working on worse and increase their business that way, you may be forced to take a whole pallet load of stuff off their hands :-).

  Note that this could turn out to be very frustrating if by chance you end up with partially cannibalized equipment without realizing it. "This VCR does not load the tape around the video drum. Come to think of it, what happened to the video drum...?" Or, "There seems to be a big hole in the front of the TV. Now, what could possibly be missing...?"

• (From: Jerry Penner (jpenner@sentex.net).)

  Make friends with several local apartment superintendants When they clean house after someone moves, they toss out all kinds of working/non-working stuff the folks left behind. Some supers make a little extra cash by fixing and reselling this stuff, some just give it the heave-ho.

Paul's Comments on the 'Well Equipped Garage or Flea Market Sale-er'

(From: Paul Grohe) grohe@galaxy.nsc.com).)

Ah! If you are really serious about buying equipment, carry one of those little 200W 120VAC inverter bricks *with you* in your backpack, along with a cigarette socket to car battery clip adapter. Keep a small marine or gel-cell battery in your car (or with a friend who has a table).

This way, when you "roll up" on a good deal, ask the seller if you can borrow his cigarette lighter, or car battery, for a few minutes. If you can't use his car (and if you have time), run back and get your battery.

If he refuses...There's your answer!

I keep an 8-cell "AA" battery holder and an assortment of pigtail power connectors in my backpack. This way, I have an adjustable 1.5 to 12V power source to test things there on the spot (I'm planning on making a complete test box, complete with ammeter and current limiting).

I also carry a bunch of "AAA" and "C" cells in my backpack ("C" cells can be shimmed into "D" holders with a few coins between the batteries).

The same rule applies, If they won't let you test it.....etc,etc,etc.

Will they give you their business card or phone number? Make it clear you will not bother them unless absolutely necessary (secretly write down their license plate number, for "Justin Case").

Also carry a pocket DMM (This is a *must* for any flea enthusiast - NEVER buy batteries w/o testing them first!) and a small, bright flashlight (for "inspections").

Smell the equipment too! This can be a big clue as to it's condition. Does it smell like something blew up? Does it smell musty or moldy?

Another clue I have found is the physical condition of the unit. Sometimes the "cleanest" unit of the bunch is the one that failed prematurely and got stuffed on a shelf or back in the box. Whereas the "used looking" units were just taken out of service.

More importantly than "functional", is "complete".

Nuthin' worse than getting something and finding out a piece, or a board, or a module, or an expensive or rare IC is missing. Now you know it's not functional, and there may be little chance of it even becoming functional again.

I always assume "dead" until happily proven otherwise. Follow your instincts! If you have doubts, there's a reason! I always consider the scrap value of the item also. Any expensive goodies in it? The power switch may be worth more than the item!

Some of my best deals were the "I don't know if it works...Oh,..five bucks" deals.

It's a gamble...Ya' win some, ya' loose some!

Caveat Emptor!!!!!

(Let duh buyer beware!)

Cheers.

And, How Paul Equipped His Home Lab

That's me! Flea Markets/Surplus Stores/Salvation Army/Goodwill/thrift stores/Garage-yard Sales/etc...And there is *lots* of good stuff around this area!

I call it "going' Junkin'".

I arrive at about 5:30 AM, so that requires a combo krypton spotlight/fluorescent lamp flashlight (a $3 Goodwill special :^).

I carry with me the aforementioned 8 cell battery pack, 8 "C" batteries, a bright krypton penlight, one of those all-in-one screwdriver/knife/pliers/scissors/bottle opener contraptions ("fishermans friend"?) and a small pocket DMM. All about 5-7 pounds total. I carry it all in a backpack that I wear "backwards" on my chest (for easy access). During the "lull" (around 9 AM), I go back and "load transfer" to the car.

I got it down to a science!! ;^)

After some lucky "scores", and a few *hundred* hours of troubleshooting, I have a *very* well stocked home lab... :^)

My home lab is graced with a Tek 576 Curve tracer (bad Xfmr), HP 5345 Freq cntr (bad NPN trannie), HP3456 DMM (bad ROM), Radiometer 106 RF Generator (stuck keys), Genrad 1688 Digital RCL meter (another bad ROM) and a "few" other assorted goodies...

The Tek 576 is my favorite. This unit was the one of the bunch that failed early and was shelved. It was dusty, dirty, full of spider webs, and missing one little knob, but in otherwise perfect shape. I got it for $200. Guys were offering me $750 for it "as-is" on the way back to the car! To top it off, two tables down from where I got the 576, someone was selling a *complete* set of the transistor/diode plug-in fixtures. Score #2!

It was a good day..... I used up all of my allocated "luck" for that year. :^)

The 576's collector supply transformers primary was dead-shorted. Eventually I was lead to Dean Kidd, who sold me a *brand new* one for $75! Tek even took the bad transformer back for failure analysis!

The HP frequency counter was the longest fix (~2 months). It's all jelly-bean TTL logic (some ECL), but no "brains" at all! Board swapping with a friends unit and some "shotgunning" brought it to back life. The eventual root failure was a single NPN transistor, in a buffer between two stages of the main 500MHz counters, whose beta had dropped significantly. I stuck a 2N2222 in there to check it out, and "there" it remains to this day!

"If it's no longer broke, Quit fixin' it!" - Paul Grohe ;^)

Everything else I have was dead, dying or crippled (er, "functionally challenged"). I even had to repair my 475A O'scope before I could use it! (It's a "P-I-T-A" to troubleshoot a scope w/o a scope!)

Too Bad About the Good Old Days

In the days before 'Weirdstuff Warehouse' stopped being weird and simply became boring, a lot of the junkus electronicus they sold bore a sticker stating:

This equipment is guaranteed not to work - should you find that it does, we will be happy to exchange it for something that doesn't.

Treat fleas the same.

(From: Paul Grohe (grohe@galaxy.nsc.com).)

Yep! I bought a lot of "goodies" with that little orange and black sticker!! I resisted the temptation to take it back if it worked. If it did work, I broke it, then fixed it, so then I would not feel so "guilty". ;^)

Harrie's Notes on Repair

Just want to share my experience on repairing electronic devices in general. After many (most successful) repairments I've concluded the following:

• If I need a schematic, then I'm really desperate, probably have spent too many hours by now on the device.

• Most of the problems were due to bad wiring between components. You must interpret this very general: bad solderdots (most common problem), bad contacts in connector, etc.

• 10 years ago and earlier, warm components were soldered with with straight leads to the solder-dots. After a few years these solder-dots come loose, or make bad contact because the leads vary in length due to temperature variations. Mostly you can see this with the bare eye. Just re-solder all big (warm) components, like transistors attached to heatsinks, big capacitors, coils etc. This works also preventive for future problems. Also, try to bend straight leads.

Take this advice in mind and I hope you can profit from it. Repair shops probably will throw a stone towards my head ;-)

Roger's Comments on Troubleshooting

The closest I ever came to bench tekking was when I would service electronic organs at a dealer's warehouse. If I spent all day there I'd normally fix upwards of 20 instruments and "check out" several others. Normally I just "ran traps" at churches, auditoriums, schools and homes where I got to five or six instruments a day.

I dealt with intermittents via a little rubber mallet and a can of cold spray!

And, I learned a couple of things:

1. 'Shotgun' a bad circuit.

2. If an amp's outputs are blown, check/replace the speakers also

3. Digital circuits are *not* logical!

4. Never hurry.

5. Check *all* supply voltages first.

6. Check all signal generation and their paths (some organs derived their rhythm section's clock from a generated note - there are similar circuits in TVs).

7. Burn-in your work - it can go out the next day.

It was a great little business until the mid '80s when the Casios and the Yamahas became popular. Now I mostly repair computers with the occasional piece of HiFi gear hitting my bench. Like that damned Sony 100-disc CD player that I can't find parts values for!

-- end V2.41 --