This is a modern Ampeg amp that develops a bad hum after about 10 minutes of operation. If you tap on the circuit board it goes away…only to come back about 30 second to a couple minutes later. Annoying for me, never mind the owner.
So the question still stands….”Which solder joint is the bad one”? It may be near impossible to even find the one single (or few) bad solder joint and take who knows how much time. I find that it is just easier (and faster which saves the owner some money) to re-flow just about every solder joint on the board. Yes, it is a bit tedious but it is the most efficient way I have found and works every time unless there are other issues. So you heat up the iron, pull up a stool and have at it…..one tiny solder joint at a time. I get lots of amps like this with similar problems and I strongly think that the tiny traces and solder pads are inadequate and issues like this are inevitable. Unfortunately this is the way things are built today….unless you go vintage or boutique. They cost more but you get more for the money….better tone, dynamics and reliability.