Some updates on the issue. It seems my motherboard is not 3126, but 3172. I don't want to go into a lot of details and bore anyone with this but i can say that it is obvious HP produced some computers which don't correlate to their handbooks at all.

florian3 wrote on 2024-09-12, 13:13:

The part in the bottom left of "current cpu front.jpg" looks like a voltage regulator with heatsink.
But before trying to use a 3.3V CPU you would definitely have to find out what JP12 does and measure the voltage.

This is correct. At least i think so. Here is why: The 3126 mobo, an older model that doesn't support 3.3V processors do not have this piece on them. Please check photo VR1 (Photo taken from https://theretroweb.com/motherboards/s/hp-vec … d3126,d3127,d31)

It's clearly written VR1 on it. And my mobo has a chip there with a heat sink as you indicated. And I may have also found a sticker that says this is actually a 3172 mobo 😀)

Long story short, I have an HP 3172 mobo which fully supports DX4/100 processors. Now the fun part. There are two jumpers which are not explained at all in the manual. JP5 and JP12. Direct quote from the manual (p.199 if interested):

"JP5 Reserved for factory use - do not move."
"JP12 (VL2 DX4 models only) Reserved for factory use - do not move."

I have no idea what exactly they are for. I combed the web as best as I could. I couldn't find any relevant info. I found some videos, hoping maybe I could catch the jumper positions but to no avail. I don't trust myself to try manually checking voltages. Even if I did, I still would need to know what these jumpers do as I am very positive that they are relevant to the issue. I think JP12 is for changing the voltage but JP5? I have no idea at all. I checked if maybe I don't need to change these jumper positions since some later DX2 models use 3.3V, nope. Mine is a 5V version. So obviously i need to change some mobo settings.

Sorry if it sounded a little bit like venting, I just feel stuck and it's a bit disappointing to have nothing after hours of searching, checking etc.

Any idea would be greatly appreciated as I am new to these subjects and maybe missing some points. Thank you very much.

Comparing the picture of your jumpers with the one on TRW, yours does have JP12 (and the VRM with heatsink) while the one on TRW is clearly missing those. JP12 mostly likely selects between 3.3V and 5V. Oddly, the WT/WB jumper is set to WB on the TRW picture even though no 486SX-33 supports WB. I'd guess that JP5 is unrelated to the CPU type given that it simply says "do not move" without any model specifics.

You could simply try it out (at your own risk), get a DX4-100, set JP12 to the other position and set WT/WB according to the CPU you have. To be sure, you'd look to see how a VL2 4/100 is set up but I haven't been able to find pictures of that either.

Sorry folks I couldn't answer earlier as I was away from internet for a while 😀

Thank you all very much for your valuable insights and suggestions. I decided not to modify with this PC any further and risk damaging it. So I will leave the original CPU in place. I decided to get a P166 PC to play high end DOS games.