Repair help

=MVS=

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 ?)

No sound

 * Backup RAM corrupt, SOUND_STOP ($D00046) is non-zero. Clear Backup RAM.
 * Power amp is dead.
 * Unplugged or faulty NEO-CDD board.

Z80 error
Can be caused by bad components / continuity with the following: Second generation specific (todo: get pin numbers in a nice table)
 * Z80 <-> SM1
 * Z80 <-> RAM
 * Z80 <-> NEO-D0 (NMI,A2-A4,IORQ)
 * Z80 <-> NEO-C1 (Z80 D0-D7)
 * NEO-D0 <-> NEO-C1 (Z80R,Z80W,Z80CLR,SDW)