DX2-66 vere the last chips without voltage markings on them (so 5V). Your BIOS likely does not know about DX4, that's why it's 3V section is not pupulated (voltage regulator should be missing as well).

Yes, you should hunt for a later board.

Thanks for the reply I thought that was the case.

I am pretty decent at electronics and had a crazy thought of populating the voltage regulator and the missing components around it.

Eh its probably not a good idea as I would not want to take the chance and mess up a working board.

Oh well thanks again!

If you can find the schematics for it and ensure that you are populating everything right, go ahead.

schematics for a 24 year old motherboard.. That would be something to see!

I did some searching for them and found nothing.
I think I would have better luck finding another user with them populated, and having them sending me pictures.
maybe i will poke around the net for high res photos and get lucky...

thanks for the idea!

Maybe someone here has the same board with regulator? You never know...

GoXoD wrote:

I am pretty decent at electronics and had a crazy thought of populating the voltage regulator and the missing components around it.

I had the same thought for my 486-gio-vp. The voltage regulator part on a 486 is not very complicated.
Not sure it's worth as you can still get later boards with PCI & all that can drive an AMD 5x86. If you do need the top end, there's also socket 7. Plentiful and still much fun.

Ya I have been staring at the board and I think All i need is a 3.3 fixed voltage reg and a 22uf tantalum cap for voltage smoothing.
I think I am going to pull the trigger and order the parts through digikey after looking at data sheets and tracing out the voltage circuit I'm pretty confident.

The main reason for this obsession is my first computer that I loved the most was a 486 dx4 100, and right now i am kind of budget restricted so i really can't order another motherboard to work with the dx4.
But I already have a super socket 7 with a amd k6 450! 😁

I am trying to build out every system that i grew up with, dos, win95/98, windows 2k, windows xp.. ect..

Just an update, I ordered the 3.3v reg and the 22uf cap it was outputting 4v for some odd reason.
I looked over the area and found two unpopulated resistor spots and it made me think I should have got an adjustable regulator not a fixed, so i tried a 5k ohm trimmer in that spot adjusted it and It is now reading 3.3141
Then I removed the trimmer checked the ohms and it was .014, So I grabbed a 0 ohm resistor dropped it in and were all good!! 3.3v for my cpu!

If anyone needs help with this / pictures just tell me.

Nicely done! And pics are always welcome 😀

Hey GoXod, any chance you could posts pics and a bit further explanation? I have the exact same 486 board and I was trying to get a 486DX4 100 working in it just like you. I didn't have one when I was a kid, but when I was still running a 386DX 33, I remember thinking that a 486DX4 100 must be SO FAST. When I got it, the board came with a 486DX2 66, but I knew I had to upgrade to the 486DX4 100.

I am not an electrical engineer. I do not know how to do circuit design. That being said, I know what a voltage regulator is and does. I know what tantalum caps are. I have recapped a number of game consoles successfully, so I'm hoping I can handle this.

I see there are a few spots where tantalum caps are missing, T1, T2 and P23. I see the open spot for a LT1085C voltage regulator. And I see the spot C97 where I'm guessing maybe you dropped in the 0 ohm resistor. Where did you install the tantalum cap? I'm guessing T2. And you mentioned you should have bought an adjustable regulator, but then with the 0 ohm resistor the voltage was outputting 3.3V as intended. Would you be willing to provide a recommended parts list?

One last question, where were you measuring to find the output was 4V rather than the expected 3.3V?