[ben]

Just a minor bump to this. Today I repaired another Series 15 with similar symptoms. Audio output was barely audible thru internal speaker. It had been stored in a damp workshop for decades. Turned out to be tin whiskers to the can on 'phase shifters' AC127 Q106 (and seemingly also on Q107, AC128,). These share the same copper heatsink. That heatsink is also a conductive path in the circuit, so you will not be able to isolate it easily or quickly. For now I have made each transistor a separate heatsink out of some tin and sound is restored.