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Help with Yamaha CR-640?

I started to disassemble it for a good cleaning and found the dried up remains of a small spider where it had fried itself between the leads of one of the 0.47 ohm emitter resistors. The resistor measures 30k, so it's open. It also smoked a 390 ohm 1/4w resistor in series with it
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Thats one badass spider to do all that damage.;)
 
timothya said:
Ok... Between pins 3 and 8 of the ouput module, I have 184mV on the right channel and 30mV on the left (DC).
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184mV !!!

This is a very high voltage. Check the 0.47 Ohm resistors on the right channel. If the 0.47 Ohm resistors are good, this means that you have ~185 mA of bias current in the output transistors. The right power module must be much warmer than the left one. Unfortunately, there is no bias adjustment in these modules and you will need to replace that one.
 
Well, this is interesting, the *other* 0.47 ohm resistor, the one that I didn't change out, now reads 88 ohms. Maybe that's what the smoke smell was that I couldn't find the source of before. Don't have time to change it out right now, but I'll do it tonight and see what happens.
 
Good to you that it is only the other resistor... At least with this large value there is no risk for the output module.
 
WooHoo! That did it! I am now giving it a test run with some flac audio from my mp3 player through my BA CR95's. Sounds great now. Next I will cross my fingers and try to get the DC offset down closer to 0.
 
Got the dc offset down to 0 on the right channel, and about 2mV on the left. Merrylander - you're right, those pots are crazy touchy.

I do believe it sounds even better now.

This is great! It's the first time I've actually fixed something electronic - even though I've got an electronic engineering degree there's a big difference between knowing all the theory and actually doing.
Thanks for all your help in this!

Now, this 30 year old receiver sounds pretty darn good, but should I consider replacing any of the caps while I've got it open?
I also have another question, but I'll start a new thread for it.
 
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Hello, I also just picked one of these things up at a flea mkt for $5.00!! one of the regulator transistors and filter caps was smoked. I replaced them and have the audio sections working nicely, but the tuner is stone dead. The large IC seems to be heating up and I can't read any numbers on it for replacement. I downloaded a free schematic but it's largely unreadable. Can anyone fill me in on what the IC is (looks like IF/MPX on the schematic) Thanks!! Ross
 
The schematic says IGO2920 or IGO2921 for the 20 pins IC. I don't know the equivalent part number for this Yamaha part...
 
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