Power amp hot on one side only

As you mention 'both heat sinks' and 'one of my power amps' it paints a picture of two stereo power amps - is this correct?

One heat sink running cold would indicate that channel not working, but you say they both sound the same.

Either that or if the power transistors are mounted to a 'transfer rail' and that rail has come away from the back of the heat sink the heat would not conduct into it.

The information given is not really sufficient for me to be able to assist.

Bipolar transistor power amps usually have all the output transistors bolted to one heat sink so that temperature foldback is easy to implement - a sort of thermal feedback that prevents the transistors going into thermal runaway and destroying themselves.

The amount of 'bias' or standing current applied causes the transistors to conduct a little (or in class A - which is really pseudo class A - conduct a lot) and they therefore have to disipate it as heat, causing the heatsink to warm.

If the mono amps are a bridged type, then there would be two power amps per amplifier, and possibly one each end. I can only speculate that if it were the case, that one amp had lost its bias or standing current for some reason or another.

I must also admit to assuming it to be bipolar transistor - it may be mosfet for all I know. I must also admit that my 'speciality' in power amps is bipolar transistors, and mosfets behave in a different way.

It looks like it's going to be a job for a repair shop... sorry, I am unable to pinpoint the fault.