It is impossible to know what caused it without examining the unit on the bench. If there was a speaker wiring error, then protection should have kicked in. If that failed you would have burn out power transistors and a blown fuse.\n\nA failure like described should never have occurred. That was dramatic and potentially dangerous. Whatever happened was probably in the high voltage section of the power supply.\n\nSo basically a user would have to really try to make that happen and it's very unlikely an error of that type is what occurred? No matter what a person might have screwed up something that catastrophic should never have happened? I'm not trying to blame op, these are questions I'd be asking myself if it happened to me too. It's not often you hear stuff like this happening.