Repair help

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Revision as of 04:32, 6 July 2011 by Furrtek (talk | contribs) (Simple VRAM error troubleshooting)
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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:

  • 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)