Here's photos of my Soyo socket 3 boards. First is a 025P2 that has a Sharp P030RV21 4-pin regulator, but also has the solder points for LT1085 or similar.
Second is a 025N2 that came without a regulator and also has some damage from the battery spill that I have to fix. Also solder points for both types of regulators.
Speaking of LT1085, I recently read about a much cheaper replacement, but forgot to write it down/bookmark the page. I think it was around here, so maybe a search will save us 😀
Later edit: found it, LM350 and LM338, recommended by stamasd

For the second board a POST card would be very helpful, I think. The CPU not getting warm could mean it is held in a RESET state, and the card would indicate that. Or maybe it doesn't receive the CLOCK signal. Do you have the tools to check for that?

Thanks for those pics. Could you post a pic that shows the surrounding area of the socket? I'll take your tips about the regulator,lk

For the second board a POST card would be very helpful, I think. The CPU not getting warm could mean it is held in a RESET state, and the card would indicate that. Or maybe it doesn't receive the CLOCK signal. Do you have the tools to check for that?

Ok i have a post-card... forgot about it 😁
So i tested it and and had reset on and no clock. I changed some jumpers and got a clock, no more always-on reset and the cpu gets warm. The card show --:--. What now? removing all the chache? I checked all the pins on the backside, straightned them, cleaned a bit... microfrtactures in some copperlines?

greetings!

HERE are the photos.

For the second board, don't really know. I heard there are boards that don't start if the battery isn't fitted, but I never encountered one. Worth checking. I'd also try with "PQFP enable" jumper in both positions, maybe function is revesed from what's written.
Also, BIOS chip, maybe corrupted? With the board unidentified, it's hard to tell. But you can try a BIOS from another board that uses the exact same chipset.

4. The clockcrystal. Shouldn't that be a 66mhz if you want to work with a DX-33/DX2-66?

dx33 is 1x33 fsb
dx2 is 2x33 fsb

so I think should work ok with the 33mhz crystal in there, probably has a jumper for clock half or full

So i had finally time to do some soldering. And it works somewhat:

First test, correct voltage.

Put in an Am486DX4-100, it boots fine. But it is recognized as a DX2 at 100Mhz.

Could it be that the bios has to be updated? I'll try an intel DX4. By the way, why is Ctbios showing ISA-bus type and not VLB?

edit:
The Intel is detected correctly. Have something similar on my Unisys ELI6 board. The amd dx4 gets recognized as a DX2-66...

greetings

Both boards:
VLB is not detected by tools like Ctbios.
It may detect ISA / EISA and possibly PCI.

II. unknown 486 ISA board:
Your unknown board does not have EISA slots, but some kind of Opti Local Bus.
Look at the BIOS chip; the sticker says "ISA BIOS".
Do not use EISA cards in it, although they fit mechanically.

Ok, i got myself an used willem programmer and dumped the BIOS of the unknown board.

Bios String: 40-0100-001266-00101111-121291-UMCAUTO 24L
Seems to been made by "Modula Tech Co."
Model "4SLUD-2.0"

Should i try some other BIOS for example "40-0100-001131-00101111-111192-UMC480 30H " having the same chipset?

greetings

edit: is there a place that collects biosdumps? I also just made 5 additional dumps of bioses i got from a colleague...

Did you ever find out more about the unknown second board? I have the same type in my possession now.

McBierle wrote on 2018-09-25, 18:11:

Thanks for looking :) <snip> II. unknown 486 ISA board The only marking i found is "4flud-1.1". I wasn't able to find it on stas […]
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Thanks for looking 😀
<snip>
II. unknown 486 ISA board
The only marking i found is "4flud-1.1". I wasn't able to find it on stason. Anyone out there got some infos?

WP_20180925_011.jpg

At first glace it looked pretty good. On closer inspection not so. Lots of pins on the backside are bend over and i found a little remaining batteryresidue. I think someone tried to restore it back to life at some point.
Strange goes one:

1. A 486DX-33 was in this socket. and as you sea there is space for a PQFP-cpu. Under the socket "P24T" is printed and in the middle of the pqfp "486DX/196".

WP_20180925_012.jpg

2. One jumper was set to PQFP-Enable.

3. If i'm not mistaken those cachechips are all together 64kb. Which diddn't fit the jumper settings (and two tag-chips), which was at 256kb. (The pic was taken after i changed it to to that setting.

WP_20180925_013.jpg

4. The clockcrystal. Shouldn't that be a 66mhz if you want to work with a DX-33/DX2-66?

I started and got nothing not even a beep. I changed the PQFP-Jumper and the cache setting and still not even a beep.
The cpu was testetd just before in the mentioned soyo-board. The CPU won't get any temperature. For the fun of it i even changed the keyboard bios, still nothing.
I will take a third even closer look at the bent pins on the backside and closly search bad solder points.

Any more ideas?

Greetings mcbierle

Sorry to post again, I looked at my board again today, it had a blown tantalum. I replaced it, it now powers on but does not POST. It hangs at POST code 13, which might be keyboard BIOS related, but I tried a known working one and it made no difference. I will hav to check my other motherboards to see if I have the exact same type.

One thing I do notice is that my keyboard BIOS chip is oriented 180 degrees different from yours. Maybe yours is in backward?

EDIT: got it working, I had my RAM in Bank 1 instead of Bank 0. Now to find a Opti Local Bus graphics card...

Hi, just now saw that you posted in here. I sold the board pretty soon after my last post.
Would be interesting if it was the keyb bios...

Greetings

Unknown no 2: Nice little board, not the fastest one but very simple to use. I have one too (bios says 4SLUD-2.0 as well) . On my board there is a 50MHz crystal placed and I run it with a DX 50 processor (not a DX/2!) And managed to get it stable with 0ws cache (20ns) and 1ws ram (8x 1MB, 70ns). So your crystal definitely must be the right one.

Little difference: mine does not have the OPTI bus slots, instead there are two regular ISA slots fitted. Looking at the markings on silk screen it was optional to choose from ISA or OPTI slot.

I got it all UMC: chipset, graphics and I/o controller. No sound card because ISA runs at 10 MHz (for 6% performance boost on graphics).

Since this unknown board is not uncommon, how are your experiences?

McBierle wrote on 2018-10-21, 17:21:

So i had finally time to do some soldering. And it works somewhat: […]
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So i had finally time to do some soldering. And it works somewhat:

WP_20181021_005.jpg
First test, correct voltage.

Put in an Am486DX4-100, it boots fine. But it is recognized as a DX2 at 100Mhz.
WP_20181021_006.jpg

WP_20181021_007.jpg

Could it be that the bios has to be updated? I'll try an intel DX4. By the way, why is Ctbios showing ISA-bus type and not VLB?

edit:
The Intel is detected correctly. Have something similar on my Unisys ELI6 board. The amd dx4 gets recognized as a DX2-66...

greetings

Hello all,
I have soldered LT1085CT voltage regulator on my SY-025K2, but my multimeter displays that VCC is 1.98V.
McBierle, did you solder anything else?

Jumpers set in 5V

Jumpers set in 3.45V

So, I have found a little bit difference between my and McBierle's motherboard. (Thanks for the first photo 😉 ) It's two resistors (R44, R45). They are placed vice versa. On my board R44 - 432 Ohm, R45 - 249 Ohm. As far as I understand they are used for adjust voltage regulator.

I just swapped them and I got 3.45V on VCC.

@Cyrix200+ a manual was found for the 4FLUD/4SLUD. I have added your photo to the page:
https://theretroweb.com/motherboards/s/modula-tech-4flud-1-1