Stephen Birchall wrote in message
...
After reading all of the issues regarding the aforementioned mixer, I
decided I had nothing to loose by taking it to pieces and attempting
to test the power output stage. On dismantling all of the plug in
units, it became apparent that both of the output boards had come
loose either by shock or vibration despite being held in by crosshead
screws. After testing the transistors, which were OK, I plugged
everything back in a couple of times to clean the contacts and hey
presto, I now have a fully functioning unit again. So it is sometimes
best to try the simple things first, before spending a fortune.
(previously an electronics engineer had told me it would cost approx
£250 to fix because on his inspection, one of the channels had been
fried. I shan't be recommending him to anyone!)

+++++++

I'm surprised they were loose. 2 ounces each and 2 screws each, and both
amps failing at the same time? or continued using with one amp only until
that failed?
Perhaps a resonance thing , one style of music , resonating with the amp
subunits

A lot of engineers are scared to even look inside these tiny class D , SMPS
, antiphase output amps and probably give a "****-off" quote