I have repaired on mkV with that symptom. It turned out to be one rectifier diode 1n4007 in the 12v voltage department that had broke down. No 12v voltage, no relay active, no life in the amp. Easy fixed though.
There might be something wrong with my mk1 mode. When I turn all tonecontrols to zero thers is still sound. Could somebody please try this. The old mk1 was a fender kind of preamp and those tone controls did not let signals trough standing at zero.