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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).

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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.

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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.

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