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Yamaha C-80 lost sound switching inputs

ghankstef said:
Ok maybe I'll do one more before putting humpty dumpty back together again.
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I was less technical at that time about ohm'ing them out. Not saying you need to. I just swamped and cycled mine 4-5 times until they acted snappy and happy. Still good after 4 years here.
:beerchug:
 
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Soundscape said:
Lol...That thing must have fallen out the truck between estate sales. :biggrin:
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No just referring to the fact that as per usual I didn't pay close enough attention to how to put it back together - like taking lots of pictures. Just started taking out screws. Not sure how to secure the volume pot and board. One day hopefully I'll learn that taking a unit apart is the easy part and take pictures and put all the screws in labeled bags.

Anyways took several tries to get the input switch board back on to the face plate correctly. I realized one cable needed to be threaded trough the hole in the input switch board and to do that had to unsolder and re-solder a cable. Then while doing that I saw that one connection from another cable was loose so I had to re-solder that and realized I had wrecked the solder pad so had to scrape to the copper in the right spot on the board and solder to that instead. But, now the input switch board is attached to the faceplate and I can hear the click when switching inputs. So hopefully this part is good to go. That's as far as I got.
 
Well frustrating - got the Yamaha preamp mostly reassembled except the cover. Did a last check on the dim bulb tester and it's bright and stays bright so it appears I have a short. 75 watt bulb Going to take longer than I had hoped.

Most recent thing I was working on was the input switch board so that is probably the place to start.

removed all the cables in the main board that connect to the input switch board but still lit up bulb

Thought the input switch board might have a bridged sollder joint. This would seem to indicate that's not the case. Photos are first off then on state for the C-80
 

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Dude...

:lurk:

Maybe excessive cleaner fluid in the tactile rails of the input switches ? I blew mine out with low pressure air.
 
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Figured it out. When replacing components due to corrosive glue near TR 149 and 150 (the ones with the heat sinks), I used 1000pf film caps instead of 100pf temporarily to see because that was what I had on hand. I ordered 100pf caps right away but then forgot to replace the 1000pf .

Thing is it was working fine as I was testing it - until it didn't.

I was looking at the voltages at tr149 and Tr150 and they were off as per the schematic.

So I then started thinking what around this part of the circuit did I muck around with? Then I remembered the caps

Put in the 100pf caps and measured tr149 and 150 again. Had correct voltages so I tested it and the sound is back.

Couple things left to do on the input board and that's it hopefully.

It is very very easy to stress the cables on the input board and pull a connection loose. Will be extra careful this time while putting it back together
 
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