Hm, I get consistent graphical corruption in specific places - 2D graphics like the Nerve Axis writing at the beginning of the Pulse demo, faces of characters in RPG games - EOB, Bloodwych, DMII etc. This has probably nothing to do with the PSU, which I suspected earlier. Is it possible that this is caused by data/filesystem corruption? Everything is on a CF card prepared in WinUAE (maybe a problem with maxtransfer or something?).
Besides this the system does all kinds of nasty things, but they can't be clearly linked with the graphical corruption issue.
Simplest thing to do is remove all boards/expansions etc.. and run the computer for a while to see what happens, adding back in one at time each peripheral until the problems occur.
It may sound like a long and boring process but it's the best way to figure out the problem. Of course, having said that and the bare machine shows up the problems then it could well be the motherboard or the PSU.
