Thank you, seems like all these kind of powered units they are OK as long as they work, but servicing is labor intensive as there is a lot to dissemble. And re-assemble! However, I found the fault which was a dry joint and it now works fine. The fault came and went if I flexed the circuit board, so a magnifying glass helped find the culprit, but I touched up the connections in the whole area with proper solder (ie lead not lead free) and now I can't make it go off again so I am happy. The Samson has been a good reliable unit generally, although the claimed 500 WPC is somewhat over optimistic,...

Thank you for the schematic I will try and fix it, the issue is that the power amps both work fine but the channels are not getting to the left master bus. It was fine yesterday, and I am hoping that it might be something simple like a loose edge connector. It did do this once before but then righted itself and has been fine for a year, but then left buss isn't getting to the LR master fader/output meter/Left power amp anymore. Thanks again.