You could be dealing with more than one problem. If you make it all the way to the green screen that usually means the Agnus chip is failing. Often a reseat will correct that. If your floppy spins endlessly, then one or both of the CIA chips could be bad. Carefully check if one seems to be running hotter than the other. Not always an accurate test, but quick and simple.
PS. I think I recall a diode, right side, at the back, edge of the mother board that could get zapped if cables were plugged incorrect in the back. So many Ami boards so many years ago, I might be mis-remembering that one though.
Plaz
