[Resolved - UniBIOS Bug] 4-Slot MVS Failure to Boot

[dillingerradio]

[SOLUTION FOLLOWS]

I gave up troubleshooting, put it all back together, and on a lark I slapped my Magical Drop 3 cart in a slot, and it worked! I didn't understand why. It turns out that UniBIOS v4.0 has a bug which can cause multi slot MVS machines to output: A black screen! (Along with some other bugs.) This would explain the frustrating several hours of troubleshooting nothing that I experienced. Go figure, eh?

Multi-slot owners are recommended to instead utilize v3.2 of UniBIOS.

Thanks, sincerely, to @ack for identifying this bug.


[ORIGINAL POST FOLLOWS]

Hello folks!

I seem to be having a run of bad luck lately! I could really use some assistance on this one, as it's been maddeningly frustrating.

On the deck is a 4-slot MVS unit.

The unit arrived exceptionally well packaged, and reported as functional. I tested the unit's four slots individually with a retail copy of Magical Drop II. To interface, I use a HAS v5 Supergun with an Arcaniac MVS to JAMMA adapter. The board booted into Unibios 2.1. Each individual slot responded appropriately and loaded the game as expected.

Satisfied with the test, I disassembled the unit. I noted the boards to be in exceptional shape and expected this to be quite a simple upgrade operation. I removed the 2.1 UniBIOS chip, and replaced it with an AT27C1024 burned with UniBIOS 4.0. I replaced the top board on the unit, and- before assembling the rest of it- I then did a power on test to verify BIOS functionality. And that's where the headache starts:

• Without a game, the unit boots immediately into an "EXCEPTION ERROR HANDLING" error (attached, has the blue box from my OSSC pro still visible).
• With a game, the unit boots to a black screen (which may eventually give way to an error, but I shut it off after a few minutes).

After seeing the error, I removed the top board and replaced the new BIOS with the original BIOS chip it came with. I then replaced the top board, and attempted to power on the unit. Rather than booting, I received an error (attached) indicating "THE SYSTEM BIOS" was the issue. I then powered off the unit, and I removed the top board from the system once more.

With the top board removed, I tried once more to boot the system, attempting to at least arrive at the system menu/test screen. It does not boot. The system behaves two different ways with the top board off, depending on the BIOS chip installed:

• If the old BIOS is installed, it fails immediately to the "THE SYSTEM BIOS" error.
• If a new BIOS chip is installed (I've burned off 2 different ones now, and verified them good in another unit), then the system black screens for several minutes and eventually pops the third error (attached, doesn't have the blue box on it.

I could definitely use some help here because this makes no sense at all to me right now. There are no cold solder joints on the BIOS. The connectors are not dirty (I've washed them with DeoxIT numerous times now).

The fact that the old BIOS suddenly doesn't work makes me feel like I'm taking crazy pills. The new BIOS is just a black screen (unless the top board is on, and then it fails immediately).

 

[ack]

The black screen is a bug in unibios 4.0 that can happen on multi-slot boards. In general I would advise against using 4.0 on multi-slot boards as there are other issues (ie audio breaks). I think most folks suggest using 3.2.

unibios does a crc check of its own rom at bootup, if that fails you will get the "THE SYSTEM BIOS" error. Given that and the other crashes I suspect you might have an address line issue between the bios chip and cpu. If you have a logic probe you could try probing all the address lines of the bios chip while the board is powered on and make sure none of them are dead. Additionally you should also try the diag bios as it has specific code for checking the upper address lines of the bios.

 

[dillingerradio]

Ahhhhhhhhhhhhhh.

Thanks for sharing that information, that's tremendously helpful. I don't have a logic probe, I'll seek one out. I also did not know a diagnostic BIOS existed. I'll seek that out and run off one of those along with the uni v3.2. Next time I pop in there to swap out the chips I'll have a run of the diag one just to verify everything's peachy and then bring it back down to v3.2 as recommended.

Cheers!

 

[xodaraP]

I recently repaired a 4 slot and installed a UniBIOS 4.0 and got the exact same error on boot

I replaced the UniBIOS IC and it worked after that and thought it might have been dirty pins causing bad contact. Good to know this is a known issue on multi slot boards. I’ll send the owner a 3.2

 

[leonk]

I wonder if this error exists with the modified Vortex UNIBIOS V4. Because that BIOS is modified, it disables all the CRC checks. This way you get all the fixes from UB4.