MV1F video RAM error, won't boot NeoDIAG BIOS.

[Kujako]

Looking at a MV1F main board, that reports a video RAM error with the stock BIOS. With the UniBIOS it reports a non-descriptive hardware failure (no memory address listed) but can then bypass the error and run as normal. When using the NeoDIAG BIOS, or when using the stock and UniBIOS without a game cartridge installed, it boot loops on the colored square screen.

I can replace the video RAM, but there's clearly something else going on as well. Any ideas?

 

[ack]

Sounds somewhat like there might be a bus conflict, but the symptoms are weird.

When you boot unibios + game and bypass the hardware check, does the game play? if it plays is it in AES or MVS mode?

For the diag bios make sure you arent using the diag bios version I posted from your mv1c thread as that would bypass normal tests and go straight to the menu system (which depends on ram). If you are running the normal diag bios try going straight to the menu system by pressing A+B+C+D, on the off chance one of the automatic tests is triggering the issue. If it makes it to the menu system try each test to see if it triggers the reboot or finds a fault.

 

[Kujako]

Sounds somewhat like there might be a bus conflict, but the symptoms are weird.

When you boot unibios + game and bypass the hardware check, does the game play? if it plays is it in AES or MVS mode?

For the diag bios make sure you arent using the diag bios version I posted from your mv1c thread as that would bypass normal tests and go straight to the menu system (which depends on ram). If you are running the normal diag bios try going straight to the menu system by pressing A+B+C+D, on the off chance one of the automatic tests is triggering the issue. If it makes it to the menu system try each test to see if it triggers the reboot or finds a fault.

Yup, using the stock Diagnostics BIOS and holding down the buttons fails to get it to post. Confirmed the EPROM I have of it still works on other systems. When I bypass the error with UniBIOS it's in Arcade/MVS mode and there are missing/corrupt graphics. Which I would expect from bad video RAM. But there does seem to be other issues....

This is the second of two of these boards I had under my workbench. Hoping to be able to get one of them that works out of the lot, but this one has me stumped. The other possibly has bad traces or other issues with the LO ROM, but this one I'm unable to diagnose.

If I (or anyone else) doesn't think of anything else to try I'll replace the video RAM this weekend and see what that does.

 

[channelmaniac]

Close up pic of the area around the battery over to the YM2610 please.

 

[Kujako]

Close up pic of the area around the battery over to the YM2610 please.

Will do, still wiring up my new video microscope rig.

Edit: looks like it's set to video not picture (shrug)

Definitely some issues (everything looks worse at high magnification). Trying to figure out where to start...

 

[channelmaniac]

Will do, still wiring up my new video microscope rig.

Each of those traces with spots on them will need to be tested for continuity. Your battery leaked and damaged them. Some of the damaged traces connect to the audio section, others connect to the Backup RAM's R/W and /OE pins. When the Backup RAM's control pins are affected they can spuriously output data and keep the system from booting.

 

[Kujako]

Each of those traces with spots on them will need to be tested for continuity. Your battery leaked and damaged them. Some of the damaged traces connect to the audio section, others connect to the Backup RAM's R/W and /OE pins. When the Backup RAM's control pins are affected they can spuriously output data and keep the system from booting.

Yup, will work on figuring out where they go.