Peavey Firebass 700. This amp is extremely loud and will do 700W at 2 ohms. I’ve had a few of these and they’ve had the same problems caused by the same thing — signal cutting out or amp actually losing power because of broken solder connections, because this thing is really loud.
It basically just sits on top of a cab intensely vibrating until some connection somewhere breaks, or many. You have to wrangle out the whole board and go through it, re-soldering anything that looks suspect. It is a pretty decent amount of work just disassembling and re-assembling it for test.