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Yamaha C-80 lost sound switching inputs

Soundscape said:
Yeah mine was humming like that too. Just like in your video. I do remember it stopped after I removed the cheap CD player I was using as a source. Sounded fine with a tuner.
EDIT: Best I can explain is...that thing is sensitive to ungrounded signals. My finger is an ungrounded signal. So yes, when I touched the front chassis, volume knob, I heard that 60Hz hum too. Try a different input source like a tuner. Put the face cover on with a screw or two. Better yet,put the bottom cover service panel back on at the metallic screw spots, especially the ones in the center riding the aluminum chassis rail, I'll bet that hum goes away.
Click to expand...
I'll try that
 
Ok some progress. Soundscape was right. Putting the bottom cover on reduced the hum to being inaudible unless I turn up the volume all the way then it's still faint.
I also tried the aux input again and it works somewhat if I tap on the loudness pot. Now the loudness and volume pots work fine on the tuner and DAD inputs so that seems to point at maybe a bad solder joint.

Phono input still has him but I wonder if just buttoning the whole thing up would take care of it. Will try it
 
Something I forgot to mention. The front panel metal chassis needs to be connected to the steel center cross support bracket. As well as the rear metal panel. I use alligator clipped jumper wires.
 
Ok more progress in the sense that yes - bottom and front plates provide grounding and hum goes away when assembled. So the hum wasn't really an issue. Live and learn! Working well enough to try it in my main system. Phono stage is working just fine. Tried the mm section actually I have a Denon 301 mc cart but I am using a step up transformer.

Didn't notice this on my bench amp but no the volume and especially the loudness pot are noisy. Loudness cuts out at certain point and is very noisy when turning it. So either I have reassembled it poorly or the volume and loudness need better cleaning. I just did squirt and pray but I think I need to figure out how to get into those pots properly and clean them
 

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Dang. Lost sound on the preamp. I went about cleaning to volume and loudness pot. There are 4 hole in the top of the enclosure so I did 3 or 4 rounds of squirt in each hole and move the volume and loudness back and forth like 100 times. They both really started to feel like they turned easily now - smooth. Then I just waited a few minutes thinking contact cleaner dries really quickly. Being excited about getting those pots cleaned I tried it out and was getting sound but the loudness pot would cut out if I turned it maybe halfway. I kept turning it back and forth and heard a loud pop at the speakers. and then no sound.

It now occurs to me there may have been a small pool of contact cleaner sitting at the bottom of the volume and loudness enclosure. Maybe it shorted out something. Turned the unit up side down to let any excess contact cleaner drain overnight. Thinking about what to do next.
 
Huh ok the volume and loudness pots really do feel smooth now but hey I'll take your word for it. . Going to have to look that up
 
Interesting turned it on this morning in the dim bub circuit and started with volume all the way down and loudness all the way to the right. Sound was back. Then tried the turning the loudness down. After turning it down about 20% sound would cut out. Then after trying that a couple times lost all sound. Really seems like that loudness pot is dirty as Avionic suggested,

Would it be worth/safe to put this bad boy in the ultrasonic cleaner instead of taking it all apart? Kind of weary of taking it apart to clean. I am good at ruining delicate things.
 
ghankstef said:
Interesting turned it on this morning in the dim bub circuit and started with volume all the way down and loudness all the way to the right. Sound was back. Then tried the turning the loudness down. After turning it down about 20% sound would cut out. Then after trying that a couple times lost all sound. Really seems like that loudness pot is dirty as Avionic suggested,

Would it be worth/safe to put this bad boy in the ultrasonic cleaner instead of taking it all apart? Kind of weary of taking it apart to clean. I am good at ruining delicate things.
Click to expand...
It sounds to me like there's a cracked carbon wafer board in the loudness gang pot. Cleaning won't fix that so I hope I'm wrong. Has this volume control taken a wack? These get damaged alot.

Can ya please post a photo of the top of the pot case to stir my memory? I do remember they're sealed and sealed for a reason. IIRC, mine had a couple holes on top to shoot in some de-ox via syringe.
 
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