Just out of warranty - distortion on one channel and crackles. Positive going excursions only on that channel, expecting blown o/p transistors but all now check out ok. They are all buried under the heatsink , so needs taking apart to monitor. Expecting bad solder, RoHS, as solder joints looking like 20 yearold leaded solder joints. No bad solder found - bad layout design. The end of a low power +B wire link ends exactly under a 3.3K 1/4W resistor laying right over it, so touching the bend of the wire. Nothing visibly wrong when received but maybe overheating of a 470R R19 resistor at a TO92 Q7 emitter. Expecting bad solder I started tapping things and phut this insignificant 3.3K , R5 at the collector of a TO92 Q1 burns up. I'm assuming its 3.3K as that was remnant measurement and corresponding channel B is 3.3K. Both these separated resistors are electrically connected in the low power section of the amp and I was the final straw.
According to the owner the amp had been overdriven for too long , outdoors, but no sign of that but perhaps enough general heat to flex something.
So for these amps bend any resistor away from the ends of any wire links.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on