Yamaha receiver RX-V681/RX-V781/RX-A760/RX-A860/TSR-7810

[ponteley]

Looking for service manual or just a amp. schematic part.

Thank you.

 

[unclejed613]

what's wrong with the amp?

 

[ponteley]

Everything working fine when plugged in and turned on.
Output voltages on all speaker terminals are few mV.
As time goes by (10-20 minutes), FR chanel goes to 10mv>100mv>200mv>300mv and up to 3V and then PROTECTION kicks in.

Very strange issue. Can't find anything blown/overheating/shorted/open.
All diodes and transistors checking out OK. Resistors too.

 

[Ylli]

I think you posted this elsewhere. As mentioned there, try freeze spray, concentrat on the input differential pair on the bad channel.

 

[ponteley]

Yes. Will try that.
Thanks.

 

[unclejed613]

also try freezing the voltage amplifier transistor, and the DC blocking cap in the feedback loop (it will be an electrolytic cap near the diff amp).