Oh my, I own the very same board and it works ... But I am missing the original bios !!

Can you please make a dump of it ? I'll add it here https://www.ultimateretro.net/motherboards/1491 (this board has been one of my motivations to make UR.net !)

I'll help you finding the reference asap !
(Funny you post this today as it's exactly two years after I found mine, October 26th 2019 Re: My Motherboard/ISA video/Big old HDD motherlode )

By the looks of it, it's indeed the transistor you need to get 3.3v (you can see that on my board it has a radiator)

It's me again, here's the best photo I could take :

It says "D45H2A" so it's definitely what you're looking for

Edit : to dump your bios, you can use this tool http://www.win3x.org/win3board/viewtopic.php?t=19455

Looks like the D45H2A is a power PNP transistor and not a stand alone regulator. I'm guessing it's controlled by the LP2951CM chip next to it, which is a low current (100mA) adjustable voltage regulator. Output voltage from the 2951 probably controls the base of the transistor, and the output from the transistor then connects to the feedback on the 2951. You may want to check the resistance of R80 and R81 as they look like they've been marked/scratched by something in the past, and they quite likely set the output voltage.

Thanks .. i Will teu to source the transistor and boot the board... Tem o Will dump the BIOS...

In a paralel question, would this board booot with no transistor if i use a 5v dx2 cpu? Or...even with 5v CPUs os the transistor nedded?

It will most likely not need the transistor for 5V CPUs.👍

Yeah it can probably take 5v from the psu

Has been difficult to find a D45H2A... mmmm.. going to try to find a replace transistor.

I think other D45H series will be ok. Check any replacement meets or exceeds the spec of the existing part (PNP, Vce>30V, Ic>8A, Ft>25MHz), and that the pins are in the right order (Base,Collector,Emitter). Did you check that R80 and R81 are ok?

Oh, and as Deksor mentioned, I'm pretty sure it'll need a heatsink on it. 5V -> 3.3V means it'll be dropping 1.7V across the transistor, which means it'll burn 1.7W per Amp drawn by the CPU. Thermal resistance between the silicon junction and free air will be around 60C/W, so the internal silicon junction will rise about 100C per Amp (60C/W * 1.7W/A) if there's no heatsink. Maximum junction temp will be around 150C. So with no heatsink the maximum current will be about 1.5A.