I actually put the two machines in the same state, removed all of the RAM, ROMs and Cache modules and floppy drives and turned them both on. The AV one CPU didn't get warm. Swapping the PSUs did nothing.

Actually the PDS slot is empty in the both machines, but that doesn't stop the 66 one to work, perhaps the AV needs the terminator?

I'll check the CPU if it's cracked. You are right about the PRAM battery, as without it, it won't output the picture.