The motherboard is a UMC OEM motherboard that appears to be made by Biostar. I posted a photo of the motherboard before. Here it is again, for this second page of the thread:
The board has no markings and the closest board I can find to it is the MB457 V1.1 as found on amoretro.de. It is not 100% identical, however, my board lacks several components found on the MB457 such as capacitors and resistors. They don't appear to have been removed, they were just never soldered on.
Here is the boot screen and BIOS string:
My attempts at trying to locate a bios update have failed.
As you can see the board's model number is MB-1433UTI. Those model leads me to several MB-1433 models produced by Biostar at one time or another but references to this particular board are nonexistant.
Here's a recount of my attempts today:
I have relocated the sound card to ISA 1, 3 and 4 and they all have the same issues. The IO card and VGA work in all 16-bit ISA slots.
I have tried disabling the LPT on the Multi IO card and it has had absolutely no effect.
I have found the issue to be that 16-bit digital audio crashes the system. Every game appears to run fine with just OPL audio. I can run DOOM with Sound Blaster music and no SFX and it will run just fine. SFX hard locks the system upon loading, usually right at the splash screen.
Running the CPU at 40MHz appears to make things worse, as at 33MHz I can run DIAGNOSE.EXE and 16-bit testing actually runs fine. If I run DIAGNOSE.EXE at 40MHz, 16-bit testing causes crashes and or screen blacking. This is leading me to believe something's not right with the ISA bus speed, as 40MHz makes it worse. There are no ISA BUS dividers on the board that I can identify and the BIOS does not present any options either.
When I run CTCU it reports no Legacy or PnP cards on my system that I can tell, there is nothing to choose, and the only IRQs selectable are 1 and 6.
I have tried to run the card with SET BLASTER=A220 I5 D1 H1 P330 T6 and SET BLASTER=A220 I5 D1 P330 T6, and the issue persists, although in this instance Doom appears to load further before locking up for whatever reason.
Kind of stuck here, and considering just getting rid of this board and doing a Pentium build instead 🙁
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