Sadly, the EP64 keeps failing, no black screens tho, only endless booting screen after pressing keys.
I suppose that there's some fault in the +9V voltage line of the bus. The controller seems to receive no power at all.
Have you checked the edge connector connections?
The motherboard (when the two screws removed) can move few millimeters in the case, and in wrong position the connection pins don't connect.
I remember from the old times, in Hungary few 100 machines were sold with the motherboard in wrong position so EXDOS didn't work with these machines. The Enterprise Service Centre corrected this problem for free.
If you removed the motherboard to assembly the expansion then possibly it is not in the right position. The best to do: attach the system bus bridge when the machine top is removed then you see the connection pins. Then fix the motherboard at the right position.
