What are the readings of the adjustments (page 3 of the service manuals) after the replacements
I'm wondering if these pots are just due for a replacement as they've always drifted. I hadn't adjusted them in a while so their measurements were:
DC Offset Left 7mv (Should be 0mv +/-5mv)
DC Offset right 10mv (Should be 0mv +/-5mv)
Bias Left 20.8mv (Should be 23mv +/-1mv)
Bias Right -18mv (Should be 23mv +/-1mv, I assume the schematics for + and - are printed incorrectly as it's not possible to set it to positive numbers)
I reset these to all within the tolerances, the amp seems to be more reliable now although it still regularly trips into protection mode.
Readjusting the DC Offset is a nightmare, even a slight tap of my screwdriver will send the value 300mv in either direction.
Also a strange thing, I noticed in this picture that a fuse had blown, I replaced the fuse but it seems to have made no impact on the protection circuit issue. I've been testing the amplifier all day and unfortunately it is still just as intermittently unreliable.
Here's some before and after photos too.
I wonder if there are some dry solder joints at play?
Also you were correct, there was one lifted solder joint, however I don't think it was causing any problems as it was still very strongly connected with the trace on the board, I glued it down with some electrically conductive glue and thickened the trace with more solder for good measure.