hifi engine

MCS Series 3865 or NEC AUA 8000 Integrated Amplifier. Needing Schematic ans service specs

I have a MCS Series 3865 amplifier with no audio out of the left channel. Upon a visual inspection inside the amp I found R405 broken at the circuit board, on what I believe is the speaker protection circuit board. It is the emitter resistor for TR 401. I'm going to replace the 470 ohm resistor and see what happens. I do not have a schematic or service manual. I am looking for these pieces of information. I'm wanting to restore this old amp. It worked flawless. My father purchased the complete MCS Series system in September of 1980. Includes the 3865 amp, 3710 tuner, 3563 cassette deck, and the 8265 speakers. he bought the 6720 turntable about a year later. This thing was BAD TO THE BONE when it was new. I'm wanting to bring it back to life. any help or input would be greatly appreciated. Thanks for reading!!



Re: MCS Series 3865 or NEC AUA 8000 Integrated Amplifier. ...

I seriously doubt the emitter resistor is 470 ohms; maybe .47 ohm.
If you have an ohmmeter (digital multimeter or VOM) you can check the good channel components. If the emitter resistor is open then the power transistors are probably bad, and possibly the driver transistors also.

Re: MCS Series 3865 or NEC AUA 8000 Integrated Amplifier. ...

Thanks Johnnysan. I did take another peek at the resistor. it;s a 4 band. Colors are; Yellow, Violet, Brown, and Gold. I checked it according to the color code and came up with 470 Ohms with 5% tolerance. I will check it again and just change out the transistors while I'm there. Thanks for the tip!!!

Re: MCS Series 3865 or NEC AUA 8000 Integrated Amplifier. ...

That may not be an emitter resistor, but in another part of the circuit. I would go to Harbour Freight and get a cheap multimeter to check those resistors. Compare the good circuit to the bad one.

Re: MCS Series 3865 or NEC AUA 8000 Integrated Amplifier. ...

I have a DVOM, I just haven't had much time this weekend to work on the amp. I posted a pic in the gallery of the resistor. TR401 is labeled on the board C B E. The emitter is tied to the same bus line on the board as R405 is. The resistor was actually broken not blown. This system spent sometime at my brothers house, I wonder if someone has been inside of it. It seems kind of odd that a resistor would just break, but I've stranger things happen before LOL. I should have some time this evening to check this out. It's been a busy weekend. I'm really wanting to get to work on this. Thanks again Johnnysan!!!