So, I came back to this board.

1) I've tried a third PSU that came with a Pentium 3@1GHz system;

2) I've removed all the hardware but CPU and RAM. At some point I've even disconnected the power from all the drives;

3) I've changed EDO RAM for FPM RAM from my 486 build (that I know to be working);

4) the chipset gets warm after 20-30 minutes, but it's not too hot to touch. Not like the Pentium Pro anyways;

5) I've checked all the jumpers. The manual says that I don't need to set the voltage since it autodetects that — but I've set that to specifically 3.3v since I'm using a Pentium Pro@200 with 256KB cache.;

6) I've tried both jumper settings for +3.3v power source;

7) I've bought a PCI/ISA POST card

Generally the LED displays are giving me -- -- (no value).

Once or twice I've got C3 05, but I can't reproduce that.

If I'll quickly turn the power off and on, I'll get 00 FF.

😎 I don't see damage to any of the capacitors (no bulging) or other components

9) the motherboard is set on a wooden board, it's not in the case anymore

What else can I try? I've got a feeling that at this point the real issue will require serious repairs that are beyond my skills (I don't know how to solder), but maybe I'm missing something simple.

jheronimus wrote:

No beep codes. The fans, LEDs and floppy/HDD/CD drives all work/make noises when connected. The CPU does get hot. Unfortunately, I already replaced the mobo with the 430HX board, so I can't test any further.

I have had exact same issue with Pentium Pro motherboard. I disconnected everything, optical drives, hdd, also pulled out everything from PCI slot. Turned to be the HDD cable is the guilty. I changed and since everything working stable.

Atom Ant wrote:

jheronimus wrote:

No beep codes. The fans, LEDs and floppy/HDD/CD drives all work/make noises when connected. The CPU does get hot. Unfortunately, I already replaced the mobo with the 430HX board, so I can't test any further.

I have had exact same issue with Pentium Pro motherboard. I disconnected everything, optical drives, hdd, also pulled out everything from PCI slot. Turned to be the HDD cable is the guilty. I changed and since everything working stable.

It's probably not the cable. If it isn't keyed and you manage to connect with it improperly, i.e. pins 39-40 to pins 1-2, the system won't boot at all and look like dead.

I'm not sure I follow. I've disconnected everything from the motherboard, so how can the drives affect it? At this point I literally have only the CPU, the RAM and the POST card in the motherboard.

CPU might be dead too.

The Serpent Rider wrote:

CPU might be dead too.

I've tried two different CPUs. I can probably try the CPU from my other Pentium Pro build, but I doubt that I've managed to find two dead Pentium Pros.

My bet is on dead CPUs or completely/partially dead CPU VRM, hence that's why no beeps and FF code on a post card.
There's also a risk that you've killed your CPUs due to the mentioned faulty VRM. Does CPU heat up blazingly fast?

jheronimus wrote:

7) I've bought a PCI/ISA POST card […]
Show full quote

7) I've bought a PCI/ISA POST card

Generally the LED displays are giving me -- -- (no value).

Once or twice I've got C3 05, but I can't reproduce that.

If I'll quickly turn the power off and on, I'll get 00 FF.

These tend to give different readings depending on how far the POST progresses before freezing. You can't really tell much with these unless it's a specific enough problem that the card always gives the same reading. I've had similar problems with a 486 board, and the culprit was the keyboard controller chip. I'd start by using a multimeter and measuring where the power reaches across the board and then start measuring individual components for faults.

If the power is fine and there is no physical damage, the only thing I can think of is the BIOS chip. Pull it out and read/write in a programming device or another mainboard. Maybe the pins need some cleaning.