According to the manual the 2.5V is for P55C CPUs which were not available at the time. It's undervolting the MMX CPU but I think it should work.

Another option could be a K6-2/3 CPU. They ran at 2.2V, but there were some models specified at 2.4V. If you have a good cooler 2,5v should be OK.

EDIT: The K6-2/3 running at 400mhz is possible since 2x multiplier is translated to 6x internally. I've tested multiple early Intel FX motherboards and have not had much problems with the K6's, but your mileage might vary.

Thanks vetz for all the advices 😀

After thinking of all options, I think I'll try to install a P200 MMX and see how it works. I see that minimum vcore for all MMX is 2.7V, so 2.5V seems not enough. But, I think I can mod this motherboard.

This is a picture of the motherboard I found on the Internet.

You can see JP32 and JP33 near the processor. Those are the jumper you have to change to get 2.5v on the vcore. Also you can see near those jumpers a big voltage regulator. I'll have to open the PC to check it, but I think that's the voltage regulator that gives 2.5V.

Maybe I could change it for another regulator that gives 2.8V.

What do you think?

LocoMJ wrote on 2020-11-07, 11:03:

Thanks vetz for all the advices :) […]
Show full quote

Thanks vetz for all the advices 😀

After thinking of all options, I think I'll try to install a P200 MMX and see how it works. I see that minimum vcore for all MMX is 2.7V, so 2.5V seems not enough. But, I think I can mod this motherboard.

This is a picture of the motherboard I found on the Internet.

You can see JP32 and JP33 near the processor. Those are the jumper you have to change to get 2.5v on the vcore. Also you can see near those jumpers a big voltage regulator. I'll have to open the PC to check it, but I think that's the voltage regulator that gives 2.5V.

Maybe I could change it for another regulator that gives 2.8V.

What do you think?

First things first, test what it's doing now. 2.5V was a very pre-pre-spec goal for the P55C, if your board actually has onboard VRM and not space for an add-in VRM module (like in the manual), it may well already output the required 2.8V.

Now, if it's 2.8V you can obviously use a P55C (why not 233MHz instead of 200MHz?). But the P55C is about the most over-engineered CPU on the planet. Even if it only outputs 2.5V, there's a good chance it will just work - those P55C things will work way out of clock and voltage spec, and undervolting is never dangerous for the hardware, at worst it could be unstable.

Now, if it is 2.5V, I'd second the K6-2 400 suggestion. There you're overvolting slightly, but given that the K6-3 ran at 2.5V anyway (and that was same core as K6-2) it's not a big issue. K6-3 is harder to find but would also add a few percent on top of K6-2 and actually run in-spec at 2.5V.

I wonder how that board actually works
Is the transistor right next to it actually made to have 2.x volt or does it have nothing to do with that ? I know many boards which have unpopulated VRM connector and nothing onboard to replace it, so it's just a 3.3V board.

By the way, where did you find that image ?

I found that image on Ebay. Maybe tomorrow I can open the PC and make some photos in detail.

I've just taken two photos of that zone in the MB, but unfortunately, to see what's the exact component, I have to disassembly all the PC and desolder that capacitor.
For the moment, I think I'll buy a Pentium MMX and try.

You can simply configure it for "2.5v" operation and measure the CPU voltage. If it's 2.5/2.8v it's good !

Hello!

Yesterday I got an Intel P200MMX FV80503200. Today I've installed it and... it works!!!

But, there is some strange "thing" in the system. I think it's because the motherboard has a very preliminary specs coded in the BIOS.

- Motherboard detects an intel P166MMX. It doesn't matter how you configure the jumpers. Always it's working at 166Mhz.

For me this is a great upgrade. Case closed.

Thanks for your advices 😀

LocoMJ wrote on 2020-11-07, 11:03:

Thanks vetz for all the advices :) […]
Show full quote

Thanks vetz for all the advices 😀

After thinking of all options, I think I'll try to install a P200 MMX and see how it works. I see that minimum vcore for all MMX is 2.7V, so 2.5V seems not enough. But, I think I can mod this motherboard.

This is a picture of the motherboard I found on the Internet.

You can see JP32 and JP33 near the processor. Those are the jumper you have to change to get 2.5v on the vcore. Also you can see near those jumpers a big voltage regulator. I'll have to open the PC to check it, but I think that's the voltage regulator that gives 2.5V.

Maybe I could change it for another regulator that gives 2.8V.

What do you think?

2.5v is enough to run 2.8 volt cpus. Back in the days these values warent very precisly, difference is only 0.3 volt..(it did not reach a few milli volts then.) But today every milli volts counts.

As long the boards delivers split voltage then you dont have going any problems.

Deksor wrote on 2020-11-07, 15:23:

I wonder how that board actually works
Is the transistor right next to it actually made to have 2.x volt or does it have nothing to do with that ? I know many boards which have unpopulated VRM connector and nothing onboard to replace it, so it's just a 3.3V board.

By the way, where did you find that image ?

I think that the base cpu voltage is always 3.3volt like always (so no VRM is installed.) If there is a VRM is installed it can do 3.3volt as well.. But also have options to lower it to the (in this case 2,5 volts)

It doesnt make any sense to replace this VRM to go from 2,5 to 2,8.. 2,5volt would work without any problem.. As someone said here above> P55C processors have a wide range voltage specification. If its some off that doesnt matter.