Yamaha C-80 problems

[RHafley]

I LOVE my vintage Yamaha gear but my C80 preamp bit it this last Sunday and I'm hoping I can post my symptoms and some of the experts here can lead me in the right diagnostic direction.

I was listening at a normal level when all within about 2 seconds I get scratchy static and then a low level hum.
I get nothing BUT the hum...out of both channels, no other sound.
The hum changes volume with the volume control
The hum is there no matter what input is selected.

I popped the top and do not see anything burned, exploded, etc. If anyone can help I'll be very grateful, thanks.

 

[OMGCat!]

Likely bad solder joints on those two transistors with the heat sinks in the middle. Also good chance a component got eaten by glue in that same area. The last C-80 I was in had a one legged film cap due to corrosion.

There are also two other transistors in the front left hand side (front of pre facing you) that like to unsolder themselves.

 

[avionic]

There are two pass transistors on a couple small heatinks. Look for dried glue corrosion around adjacent component leads. Also eyeball there solder connections for possible cracks in the solder connection. There are also numerous copper buss bars that develop cold solder connections.

 

[RHafley]

Thanks! I'll dig in this weekend and report back.

 

[Asmodeus2112]

How's it go? Looking at picking up a C-80 and curious.