UniBIOS black screen issue / board repair WIP

Got an MV-1B I'm trying to revive, replaced the Backup RAMs, the 74HC32 and D4990, also reflowed the WRAM chips. It boots to stuck on green error with original BIOS. I can't ever seem to get past the stuck on green issue on MVS boards. Original BIOS doesn't report any other errors.

I tried a UniBIOS 3.2 with NeoBiosMasta adapter. Sometimes it says Backup RAM error, but 90% of the time the MVS board turns on to a black screen, with a flickering pixel or two. If I flip all hard dips on, it says Work RAM Test, sits there forever.

Is this a problem with the UniBIOS or the MVS board?

Did you try the diagnostics BIOS? also, stuck on green usually means calendar error, but I think you already know that. Did you check the crystal that is around the backup area?

Regards.

My EPROM burner doesn't support 16-bit EPROMs, so no I haven't tried a Diagnostic BIOS. I was under the impression the UniBIOS skips calendar errors. I wanted to see if this MVS board is even working past that error.

It skips only Z80 errors iirc. Did you need me to burn you a D-bios?

If the BRAM, WRAM, D4990, Crystal, LS/HC32 and the Q1(?) transistor have all been replaced that only leaves the F0(if the MV1B has one).

Well it's possible my 32.768KHz crystals aren't any good. If I were to buy a Diag BIOS from you, you got any good crystals on hand too?

Where would the Q1 transistor be? The battery-marked area is very simplistic on the MV-1B.

HeavyMachineGun said:

Well it's possible my 32.768KHz crystals aren't any good. If I were to buy a Diag BIOS from you, you got any good crystals on hand too?

Where would the Q1 transistor be? The battery-marked area is very simplistic on the MV-1B.

Click to expand...

I should have some, I remember buying some when I was fixing MV1Cs. As for the transistor, it's the one that controls the /CE line on the BRAM. If there is a transistor in the area and the output is tied to those pins then that's the one.

Ah okay I see it now, on the solder side of the PCB. How does one tell if it's bad? What sort of transistor should I replace it with?