LT1587 seems to be 1.5V regulator. should not be relevant to the CPU voltage.

There's a thread to convert non-GX4 (5V only) to GX4 (3.3V and 5V capable): Another high-end 486 back in action (ASUS GX4 conversion success! Tons of pictures)
Unfortunately all the images are lost...

C1 is missing, near the power connector ?

Also, some tantalum capacitors are really big. check for shorts.

check pins lifted in the chip.

recheck the jumpers

I've read that this board has some sort of automatic voltage adjustment when a CPU is installed. Is that true? I don't want to fry a 3.45V CPU by chance. Any way to test for sure?

There has been some progress. The main chipset had several lifted pins, so I reflowed the entire chip and the system now POSTs.

I installed a Cyrix 40 MHz CPU (5 V, so the voltage issue is not a concern for now). The CPU is detected correctly, the system counts the RAM, and then it hangs. The diagnostic card shows POST codes 32 / 31.

I’m still suspicious about the previous recap work. When comparing my board to photos on RetroWeb, I noticed that some tantalum capacitors appear to be swapped in size — larger ones where smaller ones should be, and vice versa.

The only capacitor values I can confirm with certainty are the ones printed on the PCB near the electrolytic capacitor: 1 µF and 10 µF. On my board, however, the larger capacitor is installed where the 1 µF should be, and the smaller one where the 10 µF should be.

I also wonder if those two capacitors are wired in parallel, in which case the exact placement might not matter — but I’m not convinced this is correct.

Anyone know the exact values of the tantalum caps?

exact value is not very important. smaller caps is better by higher frequency, this is why combination with varios capacity.

autodectection works on SVG2X4, but you should put jumper as like DX4 /5x86 setting , then is autodectetion is enabled ( and only later Revision can "forcing 3.3V suppling" )
Because cyrix DX2 3.3V use S4-Pin (normally volt-det) for INVALID-signal (writeback)

early as like my SV2G4X Rev 1.2 hasn't 3.3V forcing -> it means -> pleas don't put cyrix DX2 3.3V CPU on this board. (Cyrix DX2 3.3V hasn't voltage-dectetion-pin )
https://github.com/matt1187/3.3V-adventure/bl … VGO12/readme.md

regards
matt

I took all the caps out. They are all 10 uF. Except for one between the ISA slots which is 4.7 uF. It seems that size is not an indication of value with this tantals.
ESR between 1-3 Ohms. Is this normal for tantals?

yes, 1-5 ohm is fine for ordinary tantal.