Sherwood RX-4109 / Insignia NS-R2000 Take Apart and Teardown

Sherwood has a huge business in the manufacture of audio equipment for others. As of this writing, that includes most of Pioneer's receiver product line (go ahead and look if you don't believe me, especially at some of Pioneer user's guides) as well as the stuff sold with Best Buy's Insignia brand printed on it.

Both of them cost more than what I wanted to spend, so I turned to eBay and found the Best Buy unit being sold new in box at a very low price from a seller not all that far from my location. The reviews were good and a cursory examination of a shelf demonstration unit's internals suggested it was at last passably well built.

The RX-4109 doesn't have reviews that are anywhere near as good as its Insignia counterpart. There are countless reports of people blowing them up in some way or another, sometimes only after a short period of time. As I said in my original review, there could be a few reasons for this: the receiver could be badly designed, users could be doing things they should not, or the users could just be ignorant. So that you won't think I'm leading you on in the (misguided?) hope that you will read this whole article, I now believe that all three possibilities are factors that might lead to this receiver's untimely demise. By itself, each one is minor—but if you add them all up, the end result may be a failed unit.

You'll note that some reviews show there to be no middle ground here. People either like this receiver or hate it.

This page aims to show you what is inside each receiver so you can make your own decision. I didn't want to descend on my new, working unit with tools, so I scoured eBay again and came up with an RX-4109 that was listed as able to power on but not working otherwise.

It cost $30 to purchase and ship it. I've spent more and gotten less, and the fact that it powered on suggested things weren't all that hopeless. $30 for an evening's worth of entertainment didn't seem too bad. Watching TV usually costs less, yet I'd admit that the internals of a stereo receiver are much more interesting than most of what's on the tube these days. If I got a working stereo receiver out of the deal, even better!

What wasn't so entertaining was waiting nearly a month before said receiver FINALLY darkened my doorway.

Oh well. I put the receiver on the kitchen table and plugged it in. Indeed it did power on. First the main power relay clicked, followed by the speaker protection relay, just as my working NS-R2000 receiver does. Okay, that's even more promising.

These units have speaker switches that let you select no, A, B or all speakers. I wonder...surely it couldn't be that simple?

I rummaged around and found some crappy car speakers with detached surrounds and crazed plastic cones. If the amplifier blew these up, it would be no loss. I pressed speaker switch A. There was a satisfying click¹ from the relay inside.

The audio came on perfectly as soon as I had tuned a station and put my finger against the antenna input. What a pleasant surprise.

I like to think that those companies who say “90% of units returned are in fine working order” are exaggerating but it's stuff like this that makes me wonder if we're not all doomed.

What the heck, I bought it to take apart, and that's exactly what I'm going to do. (Some of the pictures here are clickable, so you can see them in a larger size.)

Popping the cover gives a clearer look at some things you can already see. There is a decently sized power transformer, two moderately sized filter capacitors and a largely empty circuit board with lots of wire shunts running over it.

The internals are pretty clean and straightforward, although there are a few artifacts and interesting structures. A lone empty socket awaits some kind of connection to be made, probably with a daughtercard of some kind. Over by the power switch, wiring runs through a sort of “bridge” circuit board that appears to do nothing other than help route the wires. This board is grounded, so perhaps it is some sort of a choke or an attempt at limiting noise.

Another connector has a daughtercard in place that provides the phono connnectivity. This, two jumper straps on the main board and a front panel button are probably the only things to separate the phono-input equipped RX-4109 from the phono-input-less RX-4105.

The power amplifier's heatsink is curiously situated. Although there is ample space for incoming cool air to come up through the bottom of the unit, the heatsink is situated such that heated air coming off of it cannot easily escape. In other words, there are no holes in the top cover directly above the heatsink. Furthermore, there also isn't much of a heatsink. I've seen heftier heatsinks in amplifiers with lower power ratings. Surely this could have been put further back on the circuit board to facilitate a larger heatsink and more airflow?

This is not the best design I've ever seen. It could aggravate any occurrence of overheating.. I saw at least one report of someone putting a fan behind the heatsink to help the power transistors stay cool. There is plenty of space to do exactly that, as a large gap separates the front panel board from the rear of the heatsink. An AC muffin fan could be wired in without undue difficulty. The power relay could be used to turn such a fan on, or if you were really feeling clever, I suppose some kind of thermal system could be used. I think Sherwood was definitely a bit on the stingy side with their heatsink.

If people who bought these receivers have indeed done such brainy things as connecting two pairs of four ohm speakers (for an effective resistance of just two ohms when everything is playing at once!) to the amplifier, then I'm not too surprised to hear of its failure. With cooling like this, even a four ohm load is probably on the edge for this unit, especially at higher volume levels.

The back of the control board has an IC on it. In later revision receivers, this is a Silan Microelectronics (website was down, it seems to be back now 05/2010) SC16315 display driver with multiple dimming level support. That is the only function it performs, so the system controller must be somewhere else. Where is it? It's not on the control board or the mostly empty main board. On the ribbon cable leading from the display, there are volume control lines, voltage lines for the IC and display panel, a few grounds and a serial data link that goes somewhere. Earlier receivers used a Sony microcontroller situated on the display board. Most of the rest of the circuitry appears to be the same between the two. It's unclear when this change took place, but if you know, please do contact me.

I still didn't see much of anything that looked like a system controller on the other side of the board. There is a Sanyo volume, balance and tone control IC (to the right in the picture above), a very small IC whose printing I could not clearly read (it looks like a serial EEPROM though I did not trace the circuit to see if that makes sense), and an NEC uPD502T (to the upper left in the picture above).

(Whoops. I forgot to take a high resolution picture of the whole board. Oh well.)

The system controller is the NEC IC...it's an off-the-shelf 8-bit microcontroller belonging to their 78K series of products. Although "uPD502T" is all that's printed on the IC, its actual part number is quite different and will show up here as soon as I check the Sherwood service manual.

Based on pin names and some random assumptions, it appears that this unused but populated connection would have an RDS decoding circuit put into place for receivers that have RDS display capability (sadly, none sold in the US market are equipped for this). I have never understood why this is—RDS is used in the US market on some FM stations. The cost difference between receivers that have the decoder and those that don't must be negligible.

I'd like to get an example of the RDS decoder board to see what's on it. If anyone has one, please, please write me an e-mail! Sherwood America wouldn't sell or send me one.

Now for the power amplifier section, or at least the transistors that make it up. The major components are 2SD1510 and 2SB2510 transistors. Of those, some studying revealed that the 2SD1510 part is said to cross reference to an NTE261. There isn't a direct cross for 2SB2510 part that I could find, but the two NTE transistors are complementary, and the complement to an NTE261 is an NTE262.

I'm not deeply familiar with the technical details of how audio power amplification works, nor do I know precisely to what class this amplifier's design belongs, but it's my belief that this amplifier design could come close to the advertised power ratings of 105 watts/channel RMS into an eight ohm load. It looks to be a push-pull design, so it will be a class B or AB amplifier--I haven't yet determined which. (Class A push-pull audio amplifiers are not an impossibility, but this page shows you why one would be very impractical.) A 65W power dissipation figure per transistor is specified in the NTE261 (and 262) datasheet, and each one will share the burden of driving the load so it seems reasonable to me when they are paired.. (Yes, I'm using the NTE part ratings, as ratings for the parts Sherwood used don't seem to be directly available. At least I could not find them.)

Interestingly, the volume dial goes up to a maximum of 62 (63 if you count the "MAX" reading.) I wonder what the calibration and units are? There's a "db" indicator in the display but it is not used.

If I'm totally off-base here, a (polite!) correction would be more than welcome. And if anyone would like to provide a better explanation than my own limited understanding can supply, I'd greatly appreciate it—even more so if you'd be willing to let me reproduce it on this page. Write me here.

The Front Panel

I realized only after tearing the receiver apart once that I'd totally forgotten to talk about the front panel in any meaningful way. The only thing I'd said anything about was the display driver IC, and that was that.

Here's my effort to fix that. Yes, I took it apart again, this time in the comfort and privacy of my house, the house I call The Roach Palace. (I call it that only half-jokingly.) Fortunately, it's not at all difficult to remove the front panel, which is a welcome relief from some things that I've had apart. A total of seven screws later, the job is done. (For those of you reading along at home and unwisely experimenting with your own RX-410x receiver, the screws are located to each side of the front panel (two per side) and three more are located at the bottom. Yes, you'll have to remove the top cover.)

What removing the front panel makes more obvious is the size of the heatsink. You can also see that the receiver can get plenty of air through the bottom.



Approximately nine (meaning that I didn't count them) screws later and one tug of the volume control dial, the circuit board will come free. There are several boards in the Sherwood badged version of this receiver, including three daughtercards that are linked to the main board. These cover the headphone plug, speaker selection buttons and power switch.



Like nearly every other board in the unit, descriptive text is printed on the board. This board is the "RX-4105 B / RX-4109B Front B'd". As the RX-4105 hasn't got a phono input, one might be left wondering how the two can use the same front panel. Well, the RX-4105 has another AUX input to take the place of the PHONO input. There are no artifacts for unused or unimplemented features on the front panel. Every place that can have a pushbutton is occupied. The volume control is a uniquely packaged rotary encoder. It actually looks like it ought to be a conventional audio taper pot, but it is not.

Perhaps the most interesting part of the unit is the display window. The display itself is a vacuum fluorescent panel, made by the Zhejiang BOE Display Technology Company, Limited. This makes me wonder just a little bit more about the "designed in USA" text printed on the receiver's back panel. I rather doubt that it was, given how many components are sourced from Chinese companies.



I tried pretty hard to get a good picture of the panel, and this was the best shot I managed. You can click it to see a bigger one (although it's blurrier). What you can quickly see is that this same display is used across a wide variety of receivers from Sherwood, and there are a lot of indicators for features that are not used in a simple stereo receiver. In case you can't read what's printed above, the top row reads "Dolby double-D, H V S, RDS, EON, TP, TA, PTY, ST, TUNED, R2, USB, MP3, REC and moon-with-a-star (to indicate sleep timer mode)". In the middle are fourteen-segment characters for free form use, such as the display of messages, the currently selected mode and the tuned frequency when listening to the radio. At the right you have the "preset area" with "PRESET, MEM, and m f t" characters, as well as two digits, one a conventional seven-segment and the other having a "spike" standing through the middle of the seven segment area.

In between the first several fourteen segment characters there are colons and decimal points. None of the colons and only one of the decimal points are used. (RDS capable receivers do support "clock time" so a pair of the colons might be used there.)

On the bottom, the following indicators are shown "DTS, ES, 96/24, NEO:6, MPEG, Dolby double-D, D, EX, Dolby double-D, PLII, x, DSP, AUTO, DIGITAL, and DIRECT". Most of these are not used--only the "direct" indicator lights when the tone controls are bypassed.

Someone certainly loved the Dolby "double D" symbol.

Even though the very most of these indicators are never used (and I suspect that most of the fourteen segment indicators are unused as well in non-RDS versions of these receivers) the pins for the characters are hooked up. At a point where I was feeling adventurous, I tried running a moistened finger along the display pins with the power on. Depending upon what was being displayed, I could get the unused segments to illuminate. There are a few pins on the display that have been cut short and are not soldered down. I suspect these coincide with the "USB, MP3, REC" indications, as these never showed any sign of life in my experiment. R2 is used with receivers that have circuitry to support a "room 2" speaker system.

Most of the indicators in the display make sense, and most are actually put to use in Sherwood's higher end equipment. The curious ones are the "USB, MP3, and m f t" indications. I suspect their use is with a receiver that would support the direct connection of a media player or memory card device, but Sherwood does not currently market anything like that. It would be kind of neat to have a receiver that would play directly from a connected MP3 player, though. I think they should bring such an idea to market--and not just the Bluetooth bridge device they market now.

As for the RDS characters, only "EON" appears never to be used in any receiver. I guess that makes sense, since EON (Enhanced Other Network) is a "traffic report" indicator. How many people travel while listening to their home stereo receiver? I doubt that very many--if any--do such a thing unless they have it set up in a camper or something.

Well, that's really about all there is to to this thing. I was curious, so I took it apart and reported on findings with some photos thrown in for a bonus. I think that Sherwood could have implemented a better cooling system for their power amplifier—and that if they had, it would probably better tolerate or even survive the connection of speakers that presented only a four ohm resistance to the amplifier. (Those who connect two pairs of four ohm speakers to this receiver are on their own. That would result in only two ohms resistance, and I've never seen a stereo receiver that claimed it could safely operate at such low resistances.)

I can say that I did finally try operating four speakers at once with this receiver. One set consisted of two Boston Acoustics bookshelf speakers and the other set were some impressively expensive Wharfedale Modus 8 speakers. Not only were all of these speakers Very Definitely Unwisely Loud with the volume turned up, but the receiver never skipped a beat while driving them at high volume levels. I'm beginning to think that some of these units are dead in the box or that people are doing things they shouldn't, or things that they would not do if they understood the repurcussions of their actions. Even with the volume cranking (44 out of a maximum of 63 on the dial) the amplifier didn't break a sweat with an ambient temperature of some 71 degrees Fahrenheit.

There are some curious differences between the RX-4109 and Best Buy's NS-R2000. The most notable of these is the ability to control every receiver function from the front panel on the NS-R2000. With the RX-4109, you cannot access some features from the front panel, such as the display dimmer. You must have the remote. Present on the NS-R2000 is a hard power switch that is not found on the RX-4109. Both units have a soft “standby” power switch.

And don't worry...no stereo receivers were harmed in the making of this web page, as you can see from the below picture, showing the once again assembled RX-4109 powered on and playing from its built in tuner. You'll have to look carefully, but the display is on. It's driving a pair of Boston Acoustics loudspeakers (not pictured).

All work was done on an ESD handling regulation compliant kitchen table. The blue carpet in the Roach Palace is also an ESD handling regulation compliant surface.