On a 478 mainboard the cpu is powered by a seperate 12V power line, while here everything including the cpu is powered by the +5V rail.
So your PSU might have a weak 5V rail and be unable to power up the SD11 mainboards while having no issues with socket 478.

OR both SD11 have bad contacts in the cpu slots due to 20+ years of storage.

majestyk wrote on 2025-05-01, 11:57:

On a 478 mainboard the cpu is powered by a seperate 12V power line, while here everything including the cpu is powered by the +5V rail.
So your PSU might have a weak 5V rail and be unable to power up the SD11 mainboards while having no issues with socket 478.

OR both SD11 have bad contacts in the cpu slots due to 20+ years of storage.

Thanks, that is actually a very good explanation. I am using a TX-850M PSU, and it has 25A on the 5V line. I dont think any other modern PSUs has more than 25A either.

Is there some trick I can do instead of buying an old PSU? I vaguely remember something about connecting several HDDs on the system to draw more power? or maybe I am just confusing this issue with something else.

Update:

I bought an Asus Slot A motherboard, and the TX-850M PSU ran it just fine. I managed to test the board will four different Slot A CPUs.

As for the FIC SD11 boards, I bought a new old stock (still sealed) PSU. If the Boards still wont run, then these FIC boards are going to be harvested for parts.

After so many years in storage, did you check if the CMOS coil cell batteries (CR2032) are still good?
I have seen about as many motherboards not want to power up at all if the CMOS battery is dead or weak as I have motherboards that will power up fine without one. So check that first.

In regards to the PowMax LP-6100x PSU: - BEWARE! BEWARE! BEWARE!
PowMax was one of the worst PSU brands back in the day. Fortunately for you, the LP-6100 -line of PSUs, if that's what it really is "under the hood" (and that's a big *IF*), is usually halfway decent, especially for 5V-heavy PCs. But like many PSUs from that era, it's probably at a point where it will need a complete recap - I suggest doing that before you even power it on, as bad caps on the 5VSB circuit in this PSU can often result in damage to the PSU (and sometimes connected hardware too.) Actually, PowMax often used some of the worst cap brands, which is part of the reason for their bad reputation (but by far, it was due to their poorly copied designs that did like to go POW... to the MAX 🤣 ... but agian, the LP-6100 line is not that bad in this regard.) Just to get an idea of what one of these looks like inside, here you go:
https://www.badcaps.net/forum/troubleshooting … ood-as-they-get

🤣! I'll just put these 2 boards and PSU back into storage and postpone testing them for now, I dont have time to recap this thing. Thanks for the warning, and btw the coin cells are all new so its not the issue.

I opened it up and it looks like the capacitors are ok. But they are Chun Shing branded capacitors, so they should be replaced anyway.

I took some photos to compare with yours. The PCB is yellowish and some brittle brown residue is seen. I dont think its electrolytic liquid, looks more like glue remnants. Also, this is a 400W version.