Service Manual MCS amp 3850

[thetimewizard]

Hello all...I am searching for a service manual for an MCS (Modular Component Systems) Amplifier model 683-3850. Any help would be appreciated. Thank you.

Brian.

[vtech]

The MCS series were made exclusively for JCPenny stores. Unless someone worked there or as an Authorized servicer and may have it, it would be rather difficult to find originals. I think they were mainly made by NEC and Technics. What is the trouble with unit? Does it use the STKxx audio modules?

[thetimewizard]

The amp no longer has output. It powers up but no signal to the speaker outputs. I had this same problem fixed about four years ago and i believe it was an IC circuit that was replaced. I took it back to the same guy who worked on it but now he says he needs the service manual and can't remember what he did before or if he had the manual before.

[vtech]

While it is next to impossible to tell for sure, it should not be that difficult to troubleshoot the "No Audio" for an experienced technician.
When it comes to Audio, there are basic checks that can be done; Does it use a STK module or use discrete outputs. How is the biasing measure. Are the voltages there, does the protection relay click? --if not why? Is it because the protection circuit is active due to DC at the outputs or may be due to a blown output? You mentioned an IC. Is it the relay protect IC that was used on many of those gener receivers?.. etc.

[thetimewizard]

Thanks for the reply and the hel[ful info. I will pass it on to the tech working on it. To be honest I think he may be getting a little senile. I have taken my electronic stuff to him for years. He is a little out of the way for me but has always been willing to work on my older stuff without bellyaching. He is currently also working on a Phase Linear 9500 CD player that one day just stopped turning on. It took me three years but I found one for parts on eBay and he is getting it woeking for me. Anyway, the protection circuit does no longer click. This is the same behaviour it exhibited four years ago when he fixed it for me. It has been working fine up until a couple weeks ago so I am assuming it is the same problem as before, but he cannot remember what he did before. You are right that he should be able to troubleshoot it easily. I really miss it and if I could find someone else to take it to that I trusted, I certainly would. I should just learn how to work on this stuff myself...if i am going to be nuts and own all this old audio stuff then I should know how to keep it going. I own a clock shop and I repair and restore old clocks for a living, how different could it be? (LOL).

[jts1957]

[thetimewizard]

I found this info on audioasylum.com:



A friend of mine just gave me his MCS integrated amp to fix. (it doesn't play) Well, the fix took a few minutes, as both output fuses were blown. They are internal and mounted on the main motherboard.

The surprises came with looking this thing over internally. Chassis and cover are heavy gauge steel, and the cooling slots on the cover have window screen on the inside to prevent kids dropping coins in there. A large and well shielded power transformer, 10,000 uF, 50 V caps, a large square rectifier module rather than discrete diodes, star grounding, a good sized heat sink, 3 pin regulator for the low voltage sections. An even bigger surprise was finding that all the wire wrap terminations were factory soldered!

Output devices were STK flat packs.

Metal front panel and the knobs are heavy machined aluminum with a plastic insert for the knurled shafts. (I did have to re-glue an insert to the shell of a knob) Along the top of the front panel was a long narrow window with LEDs for input indication and two horizontal LED power output indicators.

No power rating, and a caution on the back to use only 8 ohm speakers, but the two outputs are in parallel. The name plate said 120W consumption, so I figure maybe 35-40 W/ch. I did not make a measurement. Output fuses are 4 amp which is 64 watts into 4 ohms.

Anyway, I hooked it to my system, and played it for an hour or so to see if the fuses would hold (they did). My second surprise was the sound. Very nice sound with my Advents. Bass was deep and tight and I'd have to say, pretty close to my NADs and my modded Onkyo integrated. Mids and highs were smooth, clear and clean. No edginess, and a fair amount of sparkle. Fine, low level detail was well rendered. Not quite as good as the Onkyo A-8190 which has a passive line stage, but close to the NAD C350.

Altogether, a much better than expected amp. Being an MCS, you could probably pick up one of these for cheap. Model number was 683-3850. Also, it's a fairly early one as the power cord and convenience outlets are not polarized, and the extra rear input says AUX instead of CD. It does have a phono section, which I didn't try. I'll report back on that!

NEC 8300A = MCS 3850 (also Curtis Mathes mentioned)http://hifigoteborg.se/Nec%208300%20A%20spec.htm

[thetimewizard]

So I guess now I am looking for a service manual for an NEC 8300A...

[thetimewizard]

So I was able to locate a manual for an NEC 8300E...does anyone know the differences between that and the NEC 8300A? Externally they appear identical. Can this manual be used for my MCS 3850/NEC 8300A?

[vtech]

There is possibility it may be the same. I think the main difference was mainly due to the output configuration. One model utilized the STKxx modules as audio output while the other would use discrete transistors for output. This was a common practice among some of the brands.
While they looked identical on the outside, it would not be the same inside.
The schematic(8300E) does NOT use the STK modules.
So the question is to look inside your unit and see which one do you have?