I've got a few system 6 mpus lying around that I'm trying to get working. Several of them will boot with masked roms, but not with burned roms. I've changed the jumper over. Using pretty standard chips, too. Do the "flipper" PROMs need to be burned as well? I've tried it both ways, but with no luck. Something is wrong, but I don't know quite what. They behave fine with leon's system 6 PROM. Ideas?