I think we're talking about separate issues.
Here we have two main issues:
1 - Sprites flickering. As Mike stated, this is highly likely due to a DRAM which has failed.
2 - Sprites misplaced. There's something stuck high/low in the ROMs 13/15/17/19. I have checked every single trace and pin and it looks like there are no shorts of sort which leads me to believe that there's something wrong with the mask roms themselves. Actually one of them has already been changed (it's different from all the others) so it might be that a bad mask rom could be the culprit.
EDIT: another thing I've checked today is the 5V voltage. I had it a bit low at 4.9V, got it back up to 5V but nothing changed.
Here we have two main issues:
1 - Sprites flickering. As Mike stated, this is highly likely due to a DRAM which has failed.
2 - Sprites misplaced. There's something stuck high/low in the ROMs 13/15/17/19. I have checked every single trace and pin and it looks like there are no shorts of sort which leads me to believe that there's something wrong with the mask roms themselves. Actually one of them has already been changed (it's different from all the others) so it might be that a bad mask rom could be the culprit.
EDIT: another thing I've checked today is the 5V voltage. I had it a bit low at 4.9V, got it back up to 5V but nothing changed.