None if the ones I've seen for repair have been used inside the speaker ,
excessive vibration causing your symptom from being used as powered speaker?
Any amp hiss from the speakers when the amp dies?
As far as I can see all the protection measures kill all power rails so no
long term continuing of any level LEDs. So what is common to both ch in the
preA ?
As there is no stereo controls with this amp , presumably the fault is
between where the inputs are commoned and where they are divided into the 2
PAs