Originally Posted by Schoenfeld
The ACA620 pushes on the sides of the 68000 pins, which bends them in slightly. If there is a cold solderjoint (which I also believe is what you're observing), the effects will be stronger with the accelerator installed.
The attached picture was taken with quite a bit of trickery with light¯o lens, so the crack is clearly seen as a shadow. Believe it or not, this A600 was working without an accelerator - exactly your case.
That does seem like a very probable cause, so I guess I know what to do next weekend.
Edit: BTW, Vesalia changed the description of the ACA620 from originally '9+1 MB' to '12+3 MB', how come? I guess it is still not possible to get more than 11.3MB available, 1MB for maprom and a bit for a freezer?