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Yamaha CR-640 Repair

I've definitely heard of this issue and I thought about it, but it often affects performance on the right side - the tuner and inputs. Fortunately my inputs are strong and the tuner is surprisingly working well.

Where I did fine a problem was with the offset pots (VR701 and VR702). Let's face it, they were $0.02 each when the receiver was built and were designed to last a year. They were flaky when they were new, but 43 years later, they're a real challenge. Even so, after the third attempt I think I found a stable notch at under 3mv on each channel.

The good news is that I got the Yamaha CR-640 working and it has been working without a shutdown now for several hours - and it sounds great. Sine waves are perfect on the scope, with the right channel showing just a tiny bit more gain than left. In either channel I have huge output, but even at 100% into dummy loads I could not see any breakup on the sine waves - very strong performance at high listening levels for sure. I measured 26ma on the right at the same time the left was putting out about 23ma, so I'm calling this good. I really like the warm sound from this receiver - almost tubular in nature. And cosmetically it looks good, all the bulbs work and the phono section is crankin' just fine. I let Pink Floyd Dark Side of the Moon Track 5 (Money) confirm.

upload_2022-8-21_13-4-10.png

Thanks to avionic and ecluser for all the help. We got it!
 
J57LITTLE said:
I've definitely heard of this issue and I thought about it, but it often affects performance on the right side - the tuner and inputs. Fortunately my inputs are strong and the tuner is surprisingly working well.

Where I did fine a problem was with the offset pots (VR701 and VR702). Let's face it, they were $0.02 each when the receiver was built and were designed to last a year. They were flaky when they were new, but 43 years later, they're a real challenge. Even so, after the third attempt I think I found a stable notch at under 3mv on each channel.

The good news is that I got the Yamaha CR-640 working and it has been working without a shutdown now for several hours - and it sounds great. Sine waves are perfect on the scope, with the right channel showing just a tiny bit more gain than left. In either channel I have huge output, but even at 100% into dummy loads I could not see any breakup on the sine waves - very strong performance at high listening levels for sure. I measured 26ma on the right at the same time the left was putting out about 23ma, so I'm calling this good. I really like the warm sound from this receiver - almost tubular in nature. And cosmetically it looks good, all the bulbs work and the phono section is crankin' just fine. I let Pink Floyd Dark Side of the Moon Track 5 (Money) confirm.

View attachment 2644452

Thanks to avionic and ecluser for all the help. We got it!
Click to expand...

I had a similar issue with a Sansui 5050 where the trimpots were difficult to adjust. You say you have it working for hours for now.....lets hope the trimpots do not move . I would play the 5050 for hours at a time then when ready to transport to the customer I would test it again one more time at my business and sure enough it act flaky again. So the next time you need to open it change those trimpots to a multi turn bourns .

Athanasios
 
Nashou66 said:
I had a similar issue with a Sansui 5050 where the trimpots were difficult to adjust. You say you have it working for hours for now.....lets hope the trimpots do not move . I would play the 5050 for hours at a time then when ready to transport to the customer I would test it again one more time at my business and sure enough it act flaky again. So the next time you need to open it change those trimpots to a multi turn bourns .

Athanasios
Click to expand...

Absolutely! I have no experience with multi-turn devices, but any more detail on this would be great!
 
I have just taken this model from a friend. It has a constant high freq noise on both channels. It can be damped with the filter but is still there. I haven't dug into it yet and am looking for some advise. This happens on all inputs. Is there a list of caps for recapping? Could old caps cause this noise? It was suggested i do a complete recapping. Would this help? Any advise would be appreciated.
 
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