Neo Geo MVS 6 Slot - Stubborn Watchdog and Click of Death
Hi Everyone,
Looking for some assistance in troubleshooting a very stubborn 6 Slot with Click of Death. Been working on this one for a few weeks now and have not been able to identify the source of the problem. Did a lot of searching on KLOV and Google but have not found anything that matches up to what I am seeing unfortunately.
- Board had very light acid damage, I patched the 3 traces that run through that area
- Continuity between ROM, CPU and RAM for all Address and Data Lines
- No physical board damage, traces are looking good (other than acid lines above)
- VIAs look and test fine. Didn't test them all of course, but all I did test were fine
- ROM is UniBIOS and works fine in other MVS boards I have
- Replaced Backup and Work RAM chips
- Replaced 68k CPU
- Clock signal to 68k looks solid (Used my scope for this)
- No chips running hot (was hoping to find a shorted chip)
- All testing is without the top board connected. My other 6 slot boots to the crosshatch without the top board connected, so assuming its ok to troubleshoot without top board connected.
Watchdog continues to reset.
The only sign of a problem I can locate is that my logic probe is showing extremely weak Address lines A5 and up. A1-A4 show solid High. The other address lines cause my logic probe to just barely register a faint click and a very faint high LED blip during the watchdog reset. I can't locate the source of the short/drain on those address lines. There are a couple of 244's and 05's that also show the low logic level at their inputs. Pulled those chips and they test just fine. No trace damage in those areas, continuity looks ok.
Would anyone have a list of troubleshooting steps to follow at this point? I'm stumped as to where the problem lies. There must be more connected to the A5 and higher address lines that i'm missing. If any photos are needed, let me know and I'll post them right away. Thanks for the assistance!
Tony
Hi Everyone,
Looking for some assistance in troubleshooting a very stubborn 6 Slot with Click of Death. Been working on this one for a few weeks now and have not been able to identify the source of the problem. Did a lot of searching on KLOV and Google but have not found anything that matches up to what I am seeing unfortunately.
- Board had very light acid damage, I patched the 3 traces that run through that area
- Continuity between ROM, CPU and RAM for all Address and Data Lines
- No physical board damage, traces are looking good (other than acid lines above)
- VIAs look and test fine. Didn't test them all of course, but all I did test were fine
- ROM is UniBIOS and works fine in other MVS boards I have
- Replaced Backup and Work RAM chips
- Replaced 68k CPU
- Clock signal to 68k looks solid (Used my scope for this)
- No chips running hot (was hoping to find a shorted chip)
- All testing is without the top board connected. My other 6 slot boots to the crosshatch without the top board connected, so assuming its ok to troubleshoot without top board connected.
Watchdog continues to reset.
The only sign of a problem I can locate is that my logic probe is showing extremely weak Address lines A5 and up. A1-A4 show solid High. The other address lines cause my logic probe to just barely register a faint click and a very faint high LED blip during the watchdog reset. I can't locate the source of the short/drain on those address lines. There are a couple of 244's and 05's that also show the low logic level at their inputs. Pulled those chips and they test just fine. No trace damage in those areas, continuity looks ok.
Would anyone have a list of troubleshooting steps to follow at this point? I'm stumped as to where the problem lies. There must be more connected to the A5 and higher address lines that i'm missing. If any photos are needed, let me know and I'll post them right away. Thanks for the assistance!
Tony
