I can tell you that at one gig, just prior to going on, my amp " died "
We then spent the next half hour eliminating all we could. We never found the answer. All cables and settings were fine, as were power supplies.
When i got back home, i plugged the amp into different cabs and it was fine. Turned out the amp went into self protection mode, and the culprit was the speakon sockets on one of my MB cabs at the gig.
Just a thought ..