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Yamaha CR 800 - crackle/fade in right channel

G

Gr8One1998

New Member
Hey all,

I have a Yamaha CR-800 that I bought a few months ago, and I'm having an issue where the right channel will crackle/scractch, and the sound fades in and out. When you turn the receiver on from a cold state, the sound in that channel is fine, but after a few minutes the symptoms come in. Here are some of the things I checked:

- This occurs on any input (phono, AUX, tuner)
- I've swapped speakers (R to L), and the issue stays with the channel, doesn't follow the speaker
- The issue presents itself with headphones as well
- I've swapped out speaker wire, no resolution
- I've cleaned all the pots with Deoxit, no resolution
- I looked at resistance and voltage at different points between the input section and the speaker terminal, and was not able to find any discrepanices between the L and R channels (I will admit that I'm a total novice when it comes to that sort of stuff)
- The left channel works perfectly

Any ideas what might be the issue here? I've tried to logic the problem out as best as I can, but have hit a dead end. I'm hoping one of you who knows a lot more about this stuff than me might have some ideas!

-Tom
 
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Could be a cold solder connection in the right channel main amplifier circuit. Tap around that area of the circuit board with a non-metallic probe. I swiped one of the wifes plastic crochet pins. While tapping listen for break ups,pops or sound cutting in and out. The lighter the tapping the easier to locate the cold solder point.


Another possibility to easily check ---
If you quickly increase then decrease the volume control does the issue clear up ? If it does, it could be the protect relay contacts are fouled.
 
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Did you get the coupler/decoupler switch on the rear panel deoxit'd ?
 
Thanks for the welcome! Yes, forgot to mention that I did hit the coupler switch with deoxit as well. I tried what you suggested; played a song until the issue was there, then increased/decreased the volume significantly. It seemed to solve the problem, but just to be sure I turned the system off and back on again after a minute or so. The problem was back, so I tried poking at the right channel section of the main amp board like you suggested. I found that when I use a probe to push in on the capacitor on the right in the picture (the one with the blue cover on it) so that it's going in further to the board, the problem disappears! It works fine as long as I push it in, and then comes back if I leave off pressure. Do you think this is a bad cap? Or is it potentially something different?
 

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Well either the cap is broken or a bad solder connection on the foil side. Either on that cap or something very close to that cap.
 
Flip it over and wiggle the cap while eyeballing the caps solder connection. If you see the caps lead wiggle reflow the solder on that connection.
 
Reflow the solder connections on those two transistors on both sides of that cap while your there.
 
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OK, tried reflowing the solder connections, and once I hooked it back up I now have no sound from either channel. There used to be a quick buzz-like sound that the receiver made about 2 or 3 seconds after turning the power on, and it's not making that sound anymore.
 
I looked and didn't see any bridges before I put the heat sync back on; is it possible that it bridged without me being able to see it?

The "buzz" sound was more of a click, yes.
 
I had done a quick visual inspection of the fuses without pulling them out right after I noticed no sound, but now after pulling them out and looking at them, 2 out of 4 are blown. I'll be off to get some fuses in the morning! I'll update tomorrow with my results. Thanks again for your help!
 
Which fuses were they ? Search AK for "dim bulb tester" It will save you trips to the store for fuses.
 
I don't see them numbered or anything, but if I'm looking at the face of the receiver and going from left to right, it would be the first and third fuses that were blown. The second and fourth were fine. I will look that up too.
 
Did you get all the mica insulators back between the transistors and the heatsink?
 
The fuses are 3 amp, 250V. 2 of the insulators did not get put back on at first; I didn't notice they were missing. They have since been put back.
 
Was this before or after the fuses blew ?.. That would definitely explain the popped fuses.
 
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