Data East Bad Dudes arcade pcb repair
Quick & easy repair – the sewer level had moving ‘dots’ that looked to be every 16 pixels up & down across the screen. In fact probably every level had these corrupt dots but the constant scrolling of the water layer in the sewer makes it more obvious.
The problem was a corrupt mask-rom for one of the tilemap layers. The ‘transparent’ tile had a corrupt bit. Burned a 27c512 eprom from the MAME data to fix it. There was no corrosion or any physical problem visible on the corrupt ROM.