More than once, I've been at the point where I'm just about to hit the amp with a sledgehammer. So then there's no question about whether it can be fixed or not, LOL. A while back in this thread, robrob made a comment regarding leaking coupling caps. I've only ever seen this once or twice with a new cap. But perhaps it's something to poke around for...I just go looking for DC after a cap. If there's a little, I note it. If there's a lot I note it. Then I go back and try to figure out if a little is OK or not (coming from some other part of the circuit). I'm not quite fluent with all the spots where a little DC offset can show up. So then I usually post here the results and wait for others to interpret.