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Yamaha CR-2020, left channel hum; right channel silent.

arhargi

arhargi

Active Member
So I finally got the relay on the power supply board to close (C817 220 uf, 63v was disconnected). Then when the FM radio station I was dialed into came up. It would only play on the left channel. Nothing is coming out of the right side.
So I went in and started looking around - even pulled the cap board back out to look at it. Didn't really find anything wrong, so I put it back together, powered-up, and NOW - left channel has a continuous hum - but it IS working. Right channel still dead. Any thoughts, ideas, or suggestions are more than welcome. Thanks.

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No it's on all inputs. I'm thinking maybe I loosened something up when I was in there checking-over the boards.
 
Check solder connection on the GND and supply wires to the cap board. Maybe use a chop stick or something non-conductive and
put a bit of pressure on each wire in turn with amp powered on, any change? If no joy then remove the cap board and check for dry
solder joints, google for pix.
 
possibility of wrong screw in a hole . well thats if different length ones are used .failing that maybe trapped wires .
 
Also, I forgot to mention - TR715 seems to be getting hot quite a bit more than TR712, for what it's worth.
 
Exercise the coupler/decoupler switch on the rear panel for the missing channel issue.That switch is notorious for being dirty and dropping channels.
 
Last edited:
petehall347 said:
possibility of wrong screw in a hole . well thats if different length ones are used .failing that maybe trapped wires .
Click to expand...
I have the relay board plugged-in to the cap board. But I haven't put the mounting screws back into the relay board yet, not until I get everything working right.
 
The relay board screws simply secure it down. They're not ground connections.
I recently re-soldered the three wires (2 - red, 1 - black) back onto the cap board, that come from the transformer. I may need to go back and double-check my soldering on those connections. That MAY be the problem with the hum.
 
Set coupler switch to off then use RCA cables, patch from Left pre out to right main in, also right pre out to left main in, ie, cross.
Right channel still dead, points to power amp, spkr selector, relay... Left channel now dead points to preamp, switches...
 
mbz said:
Set coupler switch to off then use RCA cables, patch from Left pre out to right main in, also right pre out to left main in, ie, cross.
Right channel still dead, points to power amp, spkr selector, relay... Left channel now dead points to preamp, switches...
Click to expand...

Well I double-checked the 2 red, and 1 black AC wires connected to the cap board from the transformer, and I still have a hum on the left channel w/sound. I criss-crossed the two RCA cables on the back and powered it up again. It didn't change a thing. I still have a hum w/sound out of the left - nothing out of the right channel.
Guess it's time to pull the R amp board and start checking thing over.
Does anyone have a list of equivalent modern transistors for those 2 amp boards?
 
For the dropped channel, same on headphones? Did you try spkr selector at "A+B"?
Could also try gently tapping the protection relay with a chopstick, any change?
 
Yes, I tried all the different speaker modes. Nada.
But one thing I DID find, after testing all of the resistors, capacitors, and transistors on the board was that C616 is dead. I had accidentally shorted the heat sink on TR611 to ground as couple days ago and it blew one of the fuses (thank God). However, I think it went through C616 which is one of those little itty bitty caps. See photo. It says 47 J and 6 D on it. In the schematic, for that cap., it says 47p/500. Does anyone know what that specifies? Is it 47uf @500v ? I have a bunch of this small button caps. Wonder if one of those smaller ones might be a good substitute! 20200627_164337.jpg
 
avionic said:
47pf
J = +/- 5% tolerance.

6D --? date code ,lot code ..
Click to expand...

Thanks avionic. I'm not really 100% certain this little thing is blown, because I'm not getting any readings on it from any of my test equipment. The only thing I get is when I switch my DMM to VAC, then I get about -29 mv. On my Capacitor Wizard I get no reading whatsoever. But I didn't get any readings from the Cap Wizard on any other of the little ceramic caps either.
Another thing, would having just this one little ceramic cap be enough to render the right channel inoperable? One wouldn't thing so, but.....
 
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