Carlsbro DX 12-2 Mixer

[peteypt]

I have an Carlsbro DX 12-2 Pa Mixer which only has one output working (there are a pair of identical amps, one left, one right) Been like it since a day after I bought it. (second hand years ago)

The line outputs work fine left and right and head jacks etc also work fine, so assume this is in the power amplification stage.
I've tested components on each amp channel board and they seem to behave idenically. Notably If volume on right channel is turned up and a hot enough signal is sent through the pa it will come out the speaker in a distorted state.

I was thinking it was going to be down to the power supply as from my
limited experience with op amps and similar circuits at uni they used to behave similarly when the powerpack or battery was removed, allowing a signal through if it was above a certain threshold.

Thanks for any advice, Pete