Video RAM error
- Address between $0000 and $7FFF: Check CXK58257 RAM chips next to GPUs.
- Address between $8000 and $86FF: Check CXK5814 RAM chips.
- Read high byte is different: check RAM chip with highest number.
- Read low byte is different: check RAM chip with lowest number.
- Read byte stuck to $FF (bad /OE ?), only a few bits different (traces cut ?), random address (floating /OE, /CE ?)
- Backup RAM corrupt, SOUND_STOP ($D00046) is non-zero. Clear Backup RAM.
- Power amp is dead.
- Unplugged or faulty NEO-CDD board.
Can be caused by bad components / continuity with the following:
- Z80 <-> SM1
- Z80 <-> RAM
Second generation specific (todo: get pin numbers in a nice table)
- Z80 <-> NEO-D0 (NMI,A2-A4,IORQ)
- Z80 <-> NEO-C1 (Z80 D0-D7)
- NEO-D0 <-> NEO-C1 (Z80R,Z80W,Z80CLR,SDW)