Your board doesn't have the regulator for converting 5V to 3.3V. You can solder one if you want to use a DX4. The reversion 4.0 you've mentioned use a LT1086CT.

https://www.alldatasheet.com/datasheet-pdf/pd … R/LT1086CT.html

Thank you for your answer!
I found this: https://www.lcsc.com/product-detail/C661217.html

Do I need to solder any other components or modify anything else?
Thank you yet again!

Arcadio wrote on 2025-09-23, 21:42:

Thank you for your answer! I found this: https://www.lcsc.com/product-detail/C661217.html […]
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Thank you for your answer!
I found this: https://www.lcsc.com/product-detail/C661217.html

Do I need to solder any other components or modify anything else?
Thank you yet again!

Looking at the pictures of the board with the regulator installed from TheRetroWeb, it seems to be using a fixed 3.3V regulator in TO-220 package (LT1086CT-3.3). The good news is that since it is fixed you don't need to install adjustment resistors, however the product on the link you found will not work in this case since it's the 12V output version (LT1086CT-12). You need the 3.3V version instead (or an equivalent LDO from another brand).

As far as other stuff you need to add, there's at least a transistor for auto-switching the output voltage (between the electrolytic cap and R78), a resistor (R73) and maybe a tantalum capacitor (C73, probably for the regulator input -- datasheet recommends 10uF) which I cannot tell if it's populated on your board.

Thank you for the detailed answer.
I didn't know the nomenclature, I believe this one should be the correct one: https://eu.mouser.com/ProductDetail/Analog-De … n5hUDq0dQ%3D%3D
The C73 capacitor is indeed already populated. I am attaching a better picture of my board.
What transistor for auto-switching do I need to ad? I am seeing the soldering points between the electrolytic cap and R78.

Thank you a lot for all of your info!

So looking at the picture of Rev 4.0 I've noticed the second regulator, just below the first one. My suggestion is to solder the first regulator and measure the voltage on both the VCC and the pins on the second regulator.

Is the regulator I posted the correct one? So I can place my order. I can measure after I solder it if everything goes well.

Thank you!

Arcadio wrote on 2025-09-24, 17:13:

Is the regulator I posted the correct one? So I can place my order. I can measure after I solder it if everything goes well.

Thank you!

Yes, that one is the fixed 3.3V version so it matches the one from the other board.

Regarding the transistor for auto-switching, it should be a MOSFET, although we cannot be 100% sure about it unless someone with a board that has that component populated can chime in. It's just supposed to switch the CPU voltage between 5V or the regulator output (3.3V) depending on the type of processor installed. On the well known ASUS VL/I-486SV2GX4 it was an NDP406BL but since that one is out of production many of us have used the more modern STP16NF06L instead based on the suggestion of user d0pefish.

I found this: https://www.lcsc.com/product-detail/C7429127. … _z=n_STP16NF06L is it the correct part?
Also, this might be a stupid question, but since I'm not an engineer, I have to ask. STP16NF06L's job is to switch automatically between 5v and 3.3v, so my question is, is there a way to switch it myself manually with the use of a soldered jumper?

Thank you!

Arcadio wrote on 2025-09-24, 18:05:

I found this: https://www.lcsc.com/product-detail/C7429127. … _z=n_STP16NF06L is it the correct part?
Also, this might be a stupid question, but since I'm not an engineer, I have to ask. STP16NF06L's job is to switch automatically between 5v and 3.3v, so my question is, is there a way to switch it myself manually with the use of a soldered jumper?

Thank you!

Yes, I think it should be possible to implement a manual solution with a jumper, but without knowing exactly how the traces and components are laid out on the board it's difficult to provide details.

Thank you for the clarification.
In that case, I will order both https://www.lcsc.com/product-detail/C7429127. … _z=n_STP16NF06L and https://eu.mouser.com/ProductDetail/Analog-De … n5hUDq0dQ%3D%3D and I will return with a follow up.

Don't forget to check the voltage for VCC pin on the socket before installing any processor on it.

http://ps-2.kev009.com/eprmhtml/eprmx/h12203.htm

Thank you for the diagram, very much appreciated!

To provide some more details on how the CPU voltage auto-detection works, at least on the ASUS board I mentioned before: on 3.3V processors such as the DX4, pin S-4 (VOLDET) is connected to ground, while older 5V CPUs leave it floating or connected to VCC (5V). The VOLDET pin basically drives the MOSFET gate, that way the transistor can be used to switch between 5V or the regulator output (3.3V) depending on the CPU you install in the socket.

Note that each board may implement this circuit in a slightly different way, that's why I mentioned that you need to know how these components are connected on your board to be sure. You can start by using a multimeter to determine where the traces go from the regulator and other nearby components.

While you figure out 3.3V, if you try Cachechk, you can see whether this BIOS programs the SiS 471, an otherwise speedy VLB chipset, in Always Dirty mode.
If it does, "Smout # / Ras #" is the chipset setting you need to change. If it's hidden, you can use a later version AMISETUP to flip it.