Yamaha CR-640 tuner drift

I picked up a Yamaha CR-640 a couple of years ago for $20 that cleaned up beautifully! Other than most of the bulbs being out (all except the leftmost "signal quality" light and the moving tuner indicator light) it looks practically new. I've kept it in my large detached garage above my workbench and it has worked great. Since last fall, though, the tuner has started drifting. After a few minutes, the tuner slowly starts to crackle and I have to adjust it one direction. Then a few minutes later, it slowly starts to crackle again and I have to adjust in the other direction. In fact, you can watch the "FM Tuning" needle and see it slowly drifting one direction then the other.

Is this something that will require an experienced tech to fix (I suspect so). Unfortunately, I am pretty sure the cost of servicing the CR-640 would be prohibitive (for me) given that it's a receiver that only gets occasional use, so if there is not an easy fix, I may try to find a new owner for it... Any Bostonian AK Yamaha fans?

EDIT: Just realized I have a photo...
 

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Hmm, no takers? I guess I'd say the likeliest thing is dirty slip contacts in the tuning capacitor. If that's the problem, it's it's likely to respond to cleaning the contacts with DeOxit or similar. As to whether that requires an experienced tech - probably not absolutely, though it reduces the chance of making things worse. I think there's a sticky on how to clean tuning contacts in the tuner forum if you want to try DIY. Or I could take a look at it, if Groton MA is convenient for you - shoot me a PM if so.

Cheers,

chazix
 
I just did a 620, which is probably similar. The first thing I'd do is look at the dial cord and make sure it's still flexible and isn't pulling the tuning cap due to a build up of tension or something. Mine was very gummed up on the knob shaft, and the cord had stretched so there was no tension in the spring anymore. The cap itself was also gummed up a bit in the bearings and gears. I'm guessing that other than those mechanical problems, there isn't much in the circuitry that's apt to go bad. Still possible, but I'd look at the mechanical stuff first.
 
Open it up and blow air through the tuning cap going lock to lock. Hopefully it just dust in the air gaps


Barney
 
... Any Bostonian AK Yamaha fans?
Yupp, yah got one here! Well Boston area anyway.

First try cleaning the tuning capacitor, follow the advice here: http://www.audiokarma.org/forums/showthread.php?t=144163

Do not use deoxit, use a non-residue contact cleaner.

If the contacts are dirty or corroded at all, this will work wonders.

That may solve your problem if you are lucky...if not then there are other possibilities.
 
Thanks guys, I read through the post on cleaning the tuning capacitor. I ordered some non-residue contact cleaner and will try it. I'll be sure to keep you posted!
 
Hopefully I'm not speaking prematurely, but I think you guys fixed my tuner problems! It took a few months, but today I finally got around to cleaning the variable capacitors with canned air and CRC QD Electronic Cleaner according to dr*audio's sticky thread. Then I lubed the junction points with Deoxit Fader F5. After giving it plenty of time to air dry, I put the cover back on, hooked everything up, and tuned it to a random station. Within a few minutes, the frequency started drifting upward and the audio started breaking up. I thought my efforts had failed. I dialed the tuner back down until the station came back in and then turned off the receiver and went to take care of some other stuff. About half an hour later, I went back and turned it back on, and this time, the tuner stayed on point for 2 straight hours! I hope it keeps up, but this is the first time in over a year that it's stayed tuned in to a station for more than 5-10 minutes! Thanks for your help, guys! I may go ahead and replace the burnt out bulbs now that it's back in working order!
 
I did speak too quickly. Twice now I've cleaned the tuning capacitor according to dr*audio's instructions. Every now and then it will hold a station for a good long while, but eventually, it will start to drift again. Same as before, it will hold a station for several minutes, then gradually drift off. If I chase it, it will hold for another several minutes then drift the other way. If I leave it alone, it will just tune in and out every few minutes. Also, about 2 or 3 times in the last year, the sound has shut off shortly after I power on the receiver, so it seems there is also something triggering the auto protection circuit. Anyway, this is clearly beyond my skill set, so if someone in the Boston area is interested in taking it home and trying to fix it, I'm happy to let you have it gratis. I'm already searching craigslist and Goodwill for another $20-ish vintage receiver to serve as a garage/workshop receiver.
 
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