To me it looks quite similar to this Soyo :
https://arvutimuuseum.ee/th99/m/S-T/31016.htm

I haven't found a BIOS for this exact Soyo board I've found, but maybe there are other BIOS available for this chipset made by Soyo ?

Miphee wrote on 2020-05-15, 20:32:

I have a 486 ISA board that finally doesn't have acid damage but it's giving me a hard time. It came without a BIOS chip so I pr […]
Show full quote

I have a 486 ISA board that finally doesn't have acid damage but it's giving me a hard time.
It came without a BIOS chip so I programmed a Sis401-2 version and it started up... but has a problem with the video adapter.
It starts with 1 long 3 short beeps indicating a bad video card but it displays a picture normally. Starts counting the RAM that displays incorrectly (1280 KB OK instead of 4 MB), then the system hangs. When I add less RAM it displays correctly. It's also slow, even the beeping is slow.
I tried 10 BIOS images so far and the ones that are working all do this, the rest immediately give 2 long 8 short beeps indicating a missing video card.
I tested it with 6 video cards, all the same.
I checked the board for damages but couldn't find one. Checked for shorts, nothing. Tried a different CPU, no change. Fiddled with the jumpers, no change. Tried installing cache, no change. Changed RAMs in all possible combinations, nothing. Even tried a hercules card but it didn't work.
What could be the problem? Anybody has the original BIOS image for this board or maybe a manual? It's similar to a Sis 020N2 board I saw online.

To resolve the slowness, press the turbo key.
EDIT: I mean turbo button.
OK, just set a jumper on the turbo switch 😁

Miphee wrote on 2020-05-15, 20:32:

I have a 486 ISA board that finally doesn't have acid damage but it's giving me a hard time. It came without a BIOS chip so I pr […]
Show full quote

I have a 486 ISA board that finally doesn't have acid damage but it's giving me a hard time.
It came without a BIOS chip so I programmed a Sis401-2 version and it started up... but has a problem with the video adapter.
It starts with 1 long 3 short beeps indicating a bad video card but it displays a picture normally. Starts counting the RAM that displays incorrectly (1280 KB OK instead of 4 MB), then the system hangs. When I add less RAM it displays correctly. It's also slow, even the beeping is slow.
I tried 10 BIOS images so far and the ones that are working all do this, the rest immediately give 2 long 8 short beeps indicating a missing video card.
I tested it with 6 video cards, all the same.
I checked the board for damages but couldn't find one. Checked for shorts, nothing. Tried a different CPU, no change. Fiddled with the jumpers, no change. Tried installing cache, no change. Changed RAMs in all possible combinations, nothing. Even tried a hercules card but it didn't work.
What could be the problem? Anybody has the original BIOS image for this board or maybe a manual? It's similar to a Sis 020N2 board I saw online.

And sorry, what does that mean?
..
Starts counting the RAM that displays incorrectly (1280 KB OK instead of 4 MB), then the system hangs. When I add less RAM it displays correctly
???
You can't add less than 4 modules on this type of mainboard.
So (more or less) the only option of having less RAM is 4 times 256kB, in total 1MB.
I doubt that you did try that.
So then the problem is the RAM, you need 4 good 30pin RAMs.

Most likely you need a BIOS that more closely fits the board. And Yes use good ram. For one: being a 486 ISA only, means an older chipset and those "two chip" high density SIMMS are typically an No-no. You need 8 chip or 9 chip matching SIMMS.

Thanks guys, I'll try fiddling with the RAM some more.

Tried 20 RAMs in every possible 4-8 configurations (these are all working fine in other 386-486 machines), still get the 1-3 beeps.
Then I installed 4 different modules pulled from another machine and it did POST, RAM counted correctly but started to make a continuous long beep and froze.
After restarting it returned to the 1-3 beeps and couldn't get it to POST again. Like it just decided to hate that RAM and refused to work with it.
Either this board is the pickiest board I have ever seen or some system chip is malfunctioning. The 85C402 gets pretty warm after a time.
Or some minor component like a dead tantalum cap is playing tricks on me.

85C401 : 27 C°
85C402 : 65 - 75 C°
Nothing special here.

Started fiddling with BIOS ROMs again.
Tried 3 variations of the 401 chipset based ROMs, couldn't even detect any of my video cards, 2-8 beep codes all the time.
Tried another ROM from a dead VESA board, it finally detects my RAM without the 1-3 beeps (I hear the memory counting sounds and the CMOS mismatch sound) but it's artifacting with every video cards I have. Diagnostic card reports that the computer is starting normally.
Never encountered such a problematic board before but maybe it's an incompatible BIOS error.

Check for cold or broken solder joints at the chipset. Power the board while applying pressure to the chips, see if anything changes. Make sure the board is on a hard and flat surface so it doesn't warp.

After trying 8 more BIOS ROMs and playing with RAMs I just ran out of ideas.
This UMC BIOS also gave the 1-3 memory error at startup, counted the 4 MB RAM as 896KB, allowed me to enter BIOS and setup boot from floppy, started artifacting at the boot screen, succesfully booted into DOS while displaying a memory driver error message then finally went rainbow.
This is the closest I got to a working computer.
It seems that it won't work without it's original BIOS.

It looks like bad video memory, since you've tried switching video cards, perhaps the ISA slots are corroded. On boards with corroded batterys Ive used vinegar + q-tips and light sandpaper. I've had at least 2 motherboards that needed their ISA slots cleaned before you got it it post. It's a long shot but it *might* do something.

mR_Slug wrote on 2020-05-16, 12:48:

It looks like bad video memory, since you've tried switching video cards, perhaps the ISA slots are corroded. On boards with corroded batterys Ive used vinegar + q-tips and light sandpaper. I've had at least 2 motherboards that needed their ISA slots cleaned before you got it it post. It's a long shot but it *might* do something.

Unfortunately it only happens with certain BIOS images. The last BIOS image was designed for a Sis471 chipset and it wasn't artifacting.
I already tried all of the ISA slots, even the 8 bit slot with an EGA card. It's not a contact/corrosion problem, this is the cleanest faulty board i've encountered that has the leaky barrell battery. So unless someone turns up with the exact same BIOS this motherboard has my chances are pletty slim.
I even tried cooling the 85C402 chip to see if overheating causes the artifacting but it had no effect.
Goes in the mistery pile for now.
Thanks for everyone's input though, appreciate it.

More like a Soyo SY-020P1. I have a picture of that on file.

Settings:
https://th99.bl4ckb0x.de/m/S-T/31348.htm

I'm not (yet I hope) finding the bios file for this thing. It seems it shares the same bios with the 020M2.

I think you were close with the Soyo SY-020N2 but must be a diff variant as all the Soyo SY-020 boards I looked at (SY-020P1/P2 SY-020M SY-020N) use that same Sis 86c401/402 chipset. One link gave this as a bios string for 020M: AMI 30-0200-DH1102-00101111-070791-SISAUTO-F. Too bad Archive org only goes back to a Sy-025 bios....

A20 line error? Try with another KBC.

evasive wrote on 2020-05-16, 19:08:

More like a Soyo SY-020P1. I have a picture of that on file.

Good on the 020P series ! Check this: https://i.ebayimg.com/images/g/2GkAAOSwQXdcgM9x/s-l1600.jpg
same board jumpers and has a sticker with 020P2

edit: changed link to image only

Is the only difference between P1 and P2 the 85c206 chip changed from SiS to Samsung? Also that ebay board looks quite stripped to me, missing oscillator, several components next to the memory chips and the external battery header looks a bit greenish. I hope it is sold as project, not as in wokring condition...

I configured the board according to the manual but the onboard markings are pretty straight-forward.
I don't know why this board is so picky when it comes to RAM and why it posts successfully after the 1-3 beeps.
The KB controller is already switched with another type from a working board but it didn't make a difference.
I can only think of 3 things:
- none of my RAMs are compatible
- the board only works with a certain BIOS version
- The system chipset gets hot because it has a partial malfunction.
Now if you could only find the correct BIOS we'd know. 😀

The person is selling listed it as "MOTHERBOARD 85C402 ISA SIMM SOCKET 80486, Condition: Open box, Price: US $176.70, Shipping: $42.20"
Hahhaaa and note the corrosion by the battery.

Am guessing #2 and #3 since you tried lots of ram. Yep need to find the proper BIOS and maybe a shorted cap or something....