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I experienced the same thing with a Bryston 14bsst amp. One channel would go rogue and get extremely hot, then the warning light would come on and shut down the amp. Sent it to Bryston repair and they said it was a bad bias and ended up replacing the entire left channel mother board (whatever that means!). It has worked perfectly since.
I would personally do a lot of turned off and disconnected resistive tests first, to not apply power again, at all.
To compare resistance point checks from one channel against the other.
That’s probably the most safe and reasonable way to proceed.
Like an emerg doctor, I only get to see lots of newly and nearly dead things. In this case, lots of blown and nearly blown power amps.
A good few thousand of blown and nearly blown amps across my desk, tells me to proceed in this manner.
Fundamentally, do not turn it on again.
(Basically, audio designs look good when engineered and built. Elegant, even. But when all one does is deal with the broken end of it, then the flaws in the the given thinking design, and execution..... become quite clear.)
Yes, speaker + terminal works:
And the picture on each channel you can see the protection pcb on standoffs:
That’s good couldn't see the daughter board in my pic
Still going to have to get to the underside of those emitters, if they aren’t +speaker
He’s going to have to get a probe onto the under side of those emitter resistors, looks real hard, unless the speaker terminal works.
Strongly suggest "insulated mini long hook-on probes", connect first then turn on, and visa versa.
Also imhififan do you have an indication which of the blue muti-turn pots is the bias one for him?
Me thinks you'll need a service manual
It looks very tight in there to get meter probes on to the emitter resistors which I can't even make out.
And there look to be blue trimpots all over the place!!, good luck finding the bias one with out the manual.
Set the DMM to resistance and measure across the collector and emitter of each of the power transistors. If it shows an ohm reading then you have a shorted transistor. This is the most likely cause of thermal overload trip.
But first disconnect the speaker wires from the amp, turn it on and see if the problem persists (to rule out a short on the load side).