We have a Europower pmp5000. It has been pretty good for us, but during our last gig, during a song, the sound totally cut out. We finally got the sound back by sliding the main volumn control up & down a few times. Why did it do this? Thanks!

Very strange behavior. Knowing the electronics within the unit, I see no reason that moving the main volume could restore operation. i tend to think that is a coincidence. Possibility the vibration of moving the control caused it to operate again. Do read the tip about PMP mixers I posted on Fixya about the hazard of channel A output if you use Speakon to 1/4 inch cables or adapters. If this happens again, try headphones and see if the signal still comes through them. There is an electronic fuse that can kill output IF the output current gets too high, but for that one you have toturn power off for some time for it to reset. Since you did not turn power off per your posting, that possibility is ruled out. Normally the sliders will NOT fail midstream and would be restored with any slight movement.