The failure of the output relays in the Venice 320 can be a really "interesting" problem.
While going between stage left and right amp racks testing individual portions of my three-way stereo system, had left and right mains randomly stop working. I had had problems with dirty output relays in the amps I was using, and after turning various amps on and off several times, the mains continued to work normally during sound checks and the opening band's set.
During the set change, someone was invited on stage to talk about some upcoming event, the speech became political, the mains cut out. I ran back to the board, expecting someone had pulled the faders down, but they were up, and all the meters and PFL indicated there should be output.
Wasn't until after having the board repaired that I learned it had output relays that can fail, while everything else in line still works.
Evidently, the random voltage fluctuations from turning the amplifiers on and off had been enough to cause the Venice 320 intermittent relay contacts to close, which led to the misdiagnosis, blaming the wrong relays..