Did you change FSB and multiplier jumpers?

What? No, I'm stupid, of course.

According to what I can decipher from THIS
http://th2chips.freeservers.com/m507/jumper/index.html
My PC doesn't actually support MMX or 233mhz. I did move enough jumpers around that I got it up to 166mhz, though, I should be able to go to 200. I'll keep playing with it and see what happens.

I'm not going to fry it by using this CPU, am I?

Set to 66Mhz fsb and 1.5 multiplier (which should be interpreted as a 3.5 multiplier)

Not going to fry it unless you have the voltage up too high.

Which of the jumpers is my FSB? Jumper 10 is AT Bus Clock Selector, but whatever I set it to, it makes no difference. I have 11 filled, 12 empty. 13 and 14 empty for a 1.5 multiplier, and I get 133mhz. If I set it to 3x multiplier, I get 166mhz. Again, jumper 10 doesn't seem to change anything whether I do 1-2 or 2-3.

EDIT: J8 is set to 1-2, which is 3.3 volts according to the jumper settings. Er, 2-3. Depending on how you look at the pictures. None of my jumpers actually specify which pin is 1

If I fill both 13 and 14, I also get 166.

My best guess is that with it set to 66mhz, the best I can do is x2.5 no matter what I set it to, as it maxes out at 166. Still a bump up from 120, but sadly not as fast as I'd hoped. Ah well, I suppose I can live with it.

Are you just looking at what the POST screen says? If so, my guess is that the BIOS just isn't reporting it properly.

Use SPEEDSYS or CPUCHK to verify the speed the CPU is running at.

That board will eventually fry a split rail cpu

It needs a VRM to run the pmmx
other option is to hack the vio to 3 volts and hope it stays stable.

Can this Pentium 100 motherboard accept Pentium MMX CPU?

Also You will need to jumper for 1.5 multiplier if you want 233mhz, you may overload the onboard power regulator at 3.3volts standard voltage.

There is a difference in how 1.5x is set on very early boards VRS more modern ones and that can prevent you from selecting it, hopefully this isn’t the case or you will need a cheater wire.

Via SPEEDSYS with jumpers 13-14 empty for 1.5x speed:

rmay635703 wrote on 2020-11-02, 20:47:

That board will eventually fry a split rail cpu […]
Show full quote

That board will eventually fry a split rail cpu

It needs a VRM to run the pmmx
other option is to hack the vio to 3 volts and hope it stays stable.

Also You will need to jumper for 1.5 multiplier if you want 233mhz, you may overload the onboard power regulator at 3.3volts standard voltage.

There is a difference in how 1.5x is set on very early boards VRS more modern ones and that can prevent you from selecting it, hopefully this isn’t the case or you will need a cheater wire.

So, taking it out would be the easiest thing to do, then?
or can I just set it to 2.5x for 166mhz and be done with it?

An interposer would also work for splitting the voltage. Not sure about the multiplier settings though as I haven't tried one on an interposer before.

Not having any access to any of these things, I put back the original Pentium-S. Only difference is since I set it to 66mhz instead of 60, at 2x I now have 133mhz instead of 120. So I coaxed a tiny bit more speed out of it. Woo.

I have that same motherboard and the fastest I ever managed out of it was an AMD K6-2 500 running at 300MHz @ 50MHz FSB. I've never tried running a 233 MMX on it, but the currently installed CPU is a K6-2 400 running at 210MHz @ 60MHz FSB.

The advice further up about the voltage etc is worth considering, but I've never had any issues running a K6-2 CPU at 3.3V. You'd think this would definitely fry either the CPU or the motherboard, but with adequate cooling it served me well for years in regular usage and the board (+ both CPUs) obviously still works fine today. Those VRM heatsinks do get quite hot however.

PTherapist wrote on 2020-11-02, 21:53:

I have that same motherboard and the fastest I ever managed out of it was an AMD K6-2 500 running at 300MHz @ 50MHz FSB. I've never tried running a 233 MMX on it, but the currently installed CPU is a K6-2 400 running at 210MHz @ 60MHz FSB.

The advice further up about the voltage etc is worth considering, but I've never had any issues running a K6-2 CPU at 3.3V. You'd think this would definitely fry either the CPU or the motherboard, but with adequate cooling it served me well for years in regular usage and the board (+ both CPUs) obviously still works fine today. Those VRM heatsinks do get quite hot however.

Good to know, I decided to continue screwing with it. The thing I can't understand is that no matter what I set the bus to, the X speed on the external input clock won't go higher than 2.5x, even when I set it to 3x.

Verify that motherboard supports split plane socket (3.3V i/o and 2.8V core).

Set clock and multiplier jumpers as Pentium 100 (Pentium 233MMX uses 1.5X jumpers to run as 3.5X internally at 66MHz bus) but set the voltage as 2.8V if motherboard supports 2.8V.

Cheers,

Welp, I put everything back exactly as it was before I started. Now it crashes and reboots in the middle of games, reboots if I try to play NFSSE, and hard locks if I try to reinstall NFSSE. I can only assume the thermal paste got f'ed somewhere along the way, or I've broken something else I'm not even aware of. Sigh.

Try reseating the RAM as well as the CPU if reseating the RAM doesn't help.

Same for any expansion cards.

Shouldn't a 233 interpret 1.5 multiplier to 3.5? That is, if set to 1.5x66 (aka 100 MHz), it should get 233?

Yeah, but his board seems to run it at 2x for some reason