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Yamaha C-80 lost sound switching inputs

G

ghankstef

Active Member
I picked up a used Yamaha C-80 for a c note. Excited to get it workng. I read the forums here and saw that typical issues included glue corroding the resistors and film caps near the power transistors in the power circuit. I had exactly that problem and so I cleaned off the the glue and replaced the 4.7k resistors and the 100pf film caps by the transistors with the heat sinks. I also cleaned the pots for the eq and phono settings. I was listening with it in a dim bulb circuit with some test speakers and amp. I was about to declare victory when I decided to test other inputs. I was using the DAD input playing music from my phone into a 3.5 to RCA cable. I turned it off and connected to the tuner input instead. All I get now is pops and crackle and to even get that I have to turn it up a ways.

So I suspect the contacts in the input selector need cleaning, or there may bad solder joints on the board for the input selectors but how the heck do you get in there? I tried the squirt and pray method to no avail. Any tips highly appreciated.
 
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ghankstef said:
I suspect the contacts in the input selector need cleaning, or there may bad solder joints
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Tactile switches need to be disassembled, and contacts cleaned. They are sealed up pretty good. Maybe it they were submerged/soaked in Deox-it you might get the cleaner where it will do any good.
Or. Maybe and ultrasonic cleaning will help?
 
There are some small screws in the back of the board I took out but that didn't help
 

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Yes this is where I am having trouble removing the front panel. I have all the screws out but the orange wires connected to the PCB board for input selection allow almost no slack
 
Follow the SM closely. There are more screws and a couple of plastic rivets you have to take off I think … C-70 is like that anyway, pretty sure it’s the same with C-80. The wires and the control board will come out together. Depending on what you want to do, the wires can remain attached.
 
ghankstef said:
Yes this is where I am having trouble removing the front panel. I have all the screws out but the orange wires connected to the PCB board for input selection allow almost no slack
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Unplug each of those brown/red/orange* cables from the main boards and volume control board.

* Yamaha used various different color schemes like yellow/green/blue cables.
 
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avionic said:
Tactile switches need to be disassembled, and contacts cleaned. They are sealed up pretty good. Maybe it they were submerged/soaked in Deox-it you might get the cleaner where it will do any good.
Or. Maybe and ultrasonic cleaning will help?
Click to expand...
I do have an ultrasonic cleaner if I can get it apart will give it a try
 
Ok there was one more screw in the center of the PCB board for the input selectors. Didn't have to undo all the cables. That let the rest of the front panel come off. Then I just got some contact cleaner in those switches and worked them a bit. Now I have sound again. Is it worth using fader lube here too?

As you might be able to see in the photo, I there isn't a super obvious hole to get contact cleaner into so I just did some spray and pray from the sides and above and that did the trick.

Last know problems are one of the beige pieces - for tape 2 - broke off. It was just sitting in there so I can super glue it back on.
Then also when I select the phono input there is a terrible hum - probably 60hz. Not sure if it will go away if a turntable is hooked up and grounded. If not need to track down what is going on there.

Thanks for all the help folks! Made a lot of progress
 

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ghankstef said:
Then also when I select the phono input there is a terrible hum - probably 60hz. Not sure if it will go away if a turntable is hooked up and grounded. If not need to track down what is going on there.
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Check over the ground solder connections on the phono input RCA jacks. Also several of the circuit board hold down screws , around the perimeter of the two main circuit boards provide a circuit board chassis ground connection. Loosen then re-tighten these screws very tight. See if this clears up your hummer. :biggrin:
 
avionic said:
Check over the ground solder connections on the phono input RCA jacks. Also several of the circuit board hold down screws , around the perimeter of the two main circuit boards provide a circuit board chassis ground connection. Loosen then re-tighten these screws very tight. See if this clears up your hummer. :biggrin:
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Will do thanks!
 
Dang don't know what happened. On the push button switches - the one on the bottom left broke off. I superglued it back on. It broke between the cap part - the beige part and the little stem it has. I glued it together pushing down for 60 seconds. Now none of the button stick down. Just before I did this they would click into place. Why would that happen?
 

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ghankstef said:
Dang don't know what happened. On the push button switches - the one on the bottom left broke off. I superglued it back on. It broke between the cap part - the beige part and the little stem it has. I glued it together pushing down for 60 seconds. Now none of the button stick down. Just before I did this they would click into place. Why would that happen?
Click to expand...
I'll bet the super glue flowed into the tactile switch. Wild guess
 
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