Capcom Ghosts and Goblins arcade pcb repair #2
The game played but background tiles were clearly wrong in places as were some of the sprites. As the game has relatively few tiles I looked in the MAME tilemap viewer first of all – the background mountains started around location 0xf0 in the viewer. It appeared the tiles from location 0xe0 and up were being drawn instead, so I wondered if bit 4 was stuck somewhere (bit 4 being 0×10 in hex which is the difference between 0xf0 and 0xe0).
Probing around the tilemap part of the schematics I found the A4 output line on the LS273 at 5A was indeed stuck low even while the input was pulsing. In fact a multi-meter showed the line was physically tied to ground rather than just logically low, so some kind of internal short. The LS273 was replaced and backgrounds were correct again.
As most of the sprites were correct I suspected the eproms – there are 3 pairs and a failure of any pair would affect some sprites but not others. Eprom 16 was indeed bad, and sprites were fixed when I burned a replacement. Underneath the sticker the reason for the failure was obvious – some kind of physical impact had smashed the die.