Omarkoman wrote on 2025-08-29, 07:36:

I set all the relevant jumpers for dx2-66 mhz cpu (33mhz, 2x multi) but i am unsure about setting voltage , supposed to be set on PS1 but i cant figure out what to set there.

Btw cpu is 3v, board offers 3.3v and 5v, is that ok?

3V is a short-hand for actually 3.3V or even 3.45V, so the 3.3V setting is the correct one. I'm afraid that "PS1 installed" means that you have to install a power regulator card into those pins. This regulator card (often, cards of this kind are called VRM: voltage regulator modules) is likely a proprietary card. There is a standard for Pentium/Pentium MMX voltage regulator cards, but I'm unaware of a standard for 486 voltage regulator cards. Unfortunately, this means you have these options unless you have that card:

• Use this board ony for 5V CPUs. In this case, the card can be substituted by jumpers as shown in the document you linked
• Obtain the 3.3V regulator card that fits this mainboard
• Reverse engineer how the CPU power supply on this board is supposed to work, and design and build your own voltage regulator card
• Do a limited reverse engineering to find out where the 5V I/O voltage pins and the 3.3V core voltage pins of the 486 processor are connected (5V I/O might be connected directly to +5V on the AT power supply connector or some pins of PS1 only, 3.3V is only connected to some pins of PS1), use an ATX power supply with an ATX->AT adapter and tap 3.3V from the ATX connector into the 3.3V pins at PS1.

With the jumpers set to 5V, you might fry your CPU, and without anything installed at PS1, the CPU is not getting any core voltage, so it will not work.

Put the multiplier to 1x and it should work. 2x is overclocking your CPU way too much and it will refuse to POST. The DX2 66's 2x multiplier is internal to it, so in the board if you put 2x multiplier it results in a total of 33x2x2 .. 132MHz.

Omarkoman wrote on 2025-08-29, 07:36:

i am unsure about setting voltage , supposed to be set on PS1 but i cant figure out what to set there.

The retroweb entry has multiple photos of the board, the regulator, and the board with the regulator installed to see what it looks like.
I don't know how feasible it is to find one, but I'd bet it's easier to just get and use a 5V CPU.

wbahnassi wrote on 2025-08-29, 09:45:

Put the multiplier to 1x and it should work. 2x is overclocking your CPU way too much and it will refuse to POST. The DX2 66's 2x multiplier is internal to it, so in the board if you put 2x multiplier it results in a total of 33x2x2 .. 132MHz.

That's wrong. The multiplier selection on that board does not affect the front side bus. It will stay at 33MHz no matter how you set it. The multiplier jumper just sets a pin for 486DX4 processors, which is used by those processors to choose between 2* (66MHz) and 3* (1000MHz) for their internal multiplier. A classic DX2 processor will just ignore that pin and use a fixed *2 multiplier, as you set. It will keep running at 2* even if the jumper is set to 3*. Newer 486DX2 processors contain the same die as the DX4 processors, so the die will support both 2* and 3* clock. I don't know whether Intel bonded the clock select input of that die to the CLKMUL pin or fixed the multiplier to 2* internally. Nevertheless, to be on the safe side, setting the clock multiplier to 2* instead of 3* for a modern DX2 processor is a safe choice.

The alternative would be an interposer adapter, which carries the CPU and a voltage converter. But a 5V DX2-66 shouldn't be that hard to find. If you wanted a DX4-100, 5V would require a DX4-100 ODPR (Overdrive Replacement)

Omarkoman wrote on 2025-08-29, 07:36:

I have this motherboard: […]
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I have this motherboard:

4 8 6 - G I O - V T 2

The manual:

https://theretroweb.com/motherboard/manual/32544.pdf

Clearly says how to setup this cpu.

I set all the relevant jumpers for dx2-66 mhz cpu (33mhz, 2x multi) but i am unsure about setting voltage , supposed to be set on PS1 but i cant figure out what to set there.

Btw cpu is 3v, board offers 3.3v and 5v, is that ok?

See photos as well of current jumper config. The board wont even post. No beeps, nothing.

https://i.postimg.cc/bqxBX2Qg/IMG-3329.jpg
https://i.postimg.cc/5fdRkmFj/IMG-3330.jpg
https://i.postimg.cc/gm67D7jf/IMG-3331.jpg
https://i.postimg.cc/gd753pzV/IMG-3332.jpg
https://i.postimg.cc/yV7r7YjH/IMG-3333.jpg
https://i.postimg.cc/x0gp8Dpb/IMG-3334.jpg
https://i.postimg.cc/Ch1PfP9r/IMG-3335.jpg

I solved this problem by connecting an ATX power supply, it has a voltage of 3.3 V. I made an adapter and the board worked with a 486 3v processor.

thank you for the replies, will do some experimenting this weekend.

A dx33 works fine and i dont have a 5v dx2-66

Would an Intel overdrive work?

5V Volt SZ935 DX2ODPR66

Would it mean i have to jumper it as P24C which suggests i need to put something in RN20 which i dont have?

Or is it just set as a dx2-66 cpu on this board?

Omarkoman wrote on 2025-09-01, 09:26:

Would an Intel overdrive work? […]
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Would an Intel overdrive work?

5V Volt SZ935 DX2ODPR66

Would it mean i have to jumper it as P24C which suggests i need to put something in RN20 which i dont have?

Or is it just set as a dx2-66 cpu on this board?

Yes, that processor should work perfectly. As it is an "ODPR" (OverDrive Processor Replacement), it is supposed to work out-of-the box in any system that currently has a DX33 installed without any change on the mainboard. It's quite likely that the standard DX2-66 configuration is equal to the DX33 configuration on your board - and if it is not, it likely doesn't matter which one you use. The key difference between the OPDR and the the normal DX2 is the heat sink glued to the ODPR. The DX33 works well enough without a heatsink given enough air for convection at ambient temperature, while the DX2-66 needs a heatsink. So to make the replacement by the overdrive processor a truly turn-key plug and play experience, Intel delivered the overdrive processor including the required heatsink.

I put the overdrive cpu in and its working perfectly.

Now I seem to have another problem. The COM ports are not working. There are no settings in BIOS, I see the jumpers and I can change those to either disable them or change the port but whatever serial ribbon cable / connector I use and also 3 different mice, the mouse does not work. The DOS driver loads correctly, no errors (and when I disable the port with jumpers the driver says does not exist correctly) but when I move the mouse around, it doesnt do anything. I also tried another ISA slot IDE controller with a COM port on it, disabled the ports on the mobo and plugged into the ISA card but it does not work. Not sure what else to try or whether the COM ports, both are dead? I never had this happen before.

btw using ctmouse dos driver which worked on all systems I have been using without problems.

Not sure how standard the COM cables are, the pinout might not match

Matth79 wrote on 2025-09-04, 16:17:

Not sure how standard the COM cables are, the pinout might not match

There are two standards. There are already a couple of threads about COM port cables here on VOGONS. The symptom sounds like the OP has the wrong type of cable.

I had the same issue with a GIO-VT board: mouse wouldn‘t work. It‘s just as mkarcher says, you‘ll need a COM cable that‘s wired correctly. Luckily I found one somewhere in my box with cables and yeah, that did the trick.