Wish I could provide you with a more technical explanation, but all I can do is to share my personal experience. Please see my disclaimer 'if your unit has such fuse holders'. The blade fuse holders (molds) that I've referenced, do tend to go bad with time, especially the ones used on the beefier TS amps. If this happens at a time of peak current demand, the amp will starve. I've seen technicians going for dirty contacts and changing relays, just to have the same symptoms again. Checking continuity of these wires with a VOM don't take much time, and may just save you lots of time, money and headaches.
He said his receive would come back if he tapped on the relay.
Maybe you don't understand the situation here.
If he removed the power cables from the amplifier then he could still have a change-over relay contact problem.
I hope this clears this up for you.
You are meandering down the wrong path is you continue to pursue this line of thought.