Customer reports that amplifier switches on but won’t click onto the source enabling it to play music.
Found that half the power supply was not working, +63V rail was missing from which 5v logic and +24v rails are derived. Thermal imagery showed that the area of the PSU board with the regulator pass through transistors was very warm, but only one side.
Discovered some resistors (R205, R208) were loose, indicating dry joints, so had to remove board to investigate further, this meant disassembly of all boards as unfortunately a prior repair had removed one of the connectors from the RH channel amp board. Also spotted a couple of sick looking capacitors in the vicinity of all that heat.
After removing lots of screws and keeping them organised, getting there!
Almost every solder joint in that area had cracked and failed… Just look how dark that area of the board has become over time too!
Two very dry caps removed (blackened and shriveled), 100V 47uF – had some 63V in stock but needed to order 100V versions:
Whilst waiting, set about reflowing all the joints in that area and inspecting the rest of the PSU board
Also swapped out the 100uF 100v caps as a precaution, probably not needed so much but was last in line in the +/- 63V supplies before disappearing off round the circuitry.
Solder joints all good underneath now. Found another couple on the input board connector as was getting intermittent relay clicking when wiggling cable, so reflowed those too and in the vicinity and everything now stable.
Quiescent current for both channels was adjusted according to service manual (18.5mV +/- 1.5mV), no load, volume 0 – set to ~17mV initially and rechecked after 20 minutes for stability.
After cleaning up the phono connectors on the back (quite dirty), all functions were tested, all inputs good.
Customer was very pleased to have their old amp back in action! When asked that it must have had some issues given all the dry joints, they said it had taken a few minutes sometimes to come on properly until it stopped altogether. It’s always better to get something fixed as soon as issues arise before further problems are caused.