There's a brown slot that is supposed to be cpu cache but I have no idea how to get one compatible.

Any COAST stick will do. Your board already has 256kB L2 PLB cache soldered onto it (those two UMC chips next to the 88243VX chip), so the only benefit of a COAST module would be to increase that to 512kB. The difference might be measurable, but almost certainly not noticeable. Tbh, I wouldn't bother.

The motherboard has a "green pc" connector but the case doesn't seem to have it.

So use any other button you have. It will put the PC into sleep mode. Not really very useful in a retro perspective.

The cpu is a socket 7, but the manual says that the pentium 166 is the maximum supported (currently pentium 133), can someone confirm?
I wanted to place a pentium 233 mmx on it.

There are a few considerations. The most important is voltage - to run a Pentium MMX the board needs to be able to supply split voltage with 2.8V for the CPU. For that you need a voltage regulator.

You post three pics here, but they are from three different boards 😮

Top is rev C with a 168p DIMM slot, middle is rev B, bottom is rev C without a 168p DIMM slot.

That is relevant here as things like voltage regulators were optional on early So7 boards (like that DIMM slot). The bottom board has two MOSFET transistors with big heatsinks at the bottom of the board. That is a linear VRM. If your board also has them you are in luck. The other pics don't show the relevant part of the board. Is at least one of these pics of your own board?

If you have the VRM, you can use J9 and J11 set to resp 1-2 and 1-2 3-4 to set the voltage to 2.8V. Then you need to set correct bus speed (66MHz, with JP6 3-4) and multiplier 3.5x on the MMX is re-mapped onto the 1.5x setting from the non-MMX, so choose JP8 open.

If you don't have the VRM, you're limited to non-MMX, so max P200. If you have one, set bus to 66MHz and multiplier to 3.0x (JP8 3-4)

dionb wrote on 2022-05-18, 18:13:

Any COAST stick will do. Your board already has 256kB L2 PLB cache soldered onto it (those two UMC chips next to the 88243VX chi […]
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There's a brown slot that is supposed to be cpu cache but I have no idea how to get one compatible.

Any COAST stick will do. Your board already has 256kB L2 PLB cache soldered onto it (those two UMC chips next to the 88243VX chip), so the only benefit of a COAST module would be to increase that to 512kB. The difference might be measurable, but almost certainly not noticeable. Tbh, I wouldn't bother.

The motherboard has a "green pc" connector but the case doesn't seem to have it.

So use any other button you have. It will put the PC into sleep mode. Not really very useful in a retro perspective.

The cpu is a socket 7, but the manual says that the pentium 166 is the maximum supported (currently pentium 133), can someone confirm?
I wanted to place a pentium 233 mmx on it.

There are a few considerations. The most important is voltage - to run a Pentium MMX the board needs to be able to supply split voltage with 2.8V for the CPU. For that you need a voltage regulator.

You post three pics here, but they are from three different boards 😮

Top is rev C with a 168p DIMM slot, middle is rev B, bottom is rev C without a 168p DIMM slot.

That is relevant here as things like voltage regulators were optional on early So7 boards (like that DIMM slot). The bottom board has two MOSFET transistors with big heatsinks at the bottom of the board. That is a linear VRM. If your board also has them you are in luck. The other pics don't show the relevant part of the board. Is at least one of these pics of your own board?

If you have the VRM, you can use J9 and J11 set to resp 1-2 and 1-2 3-4 to set the voltage to 2.8V. Then you need to set correct bus speed (66MHz, with JP6 3-4) and multiplier 3.5x on the MMX is re-mapped onto the 1.5x setting from the non-MMX, so choose JP8 open.

If you don't have the VRM, you're limited to non-MMX, so max P200. If you have one, set bus to 66MHz and multiplier to 3.0x (JP8 3-4)

Thanks for the reply.
The top image is mine in the previous post.
The others were because I preferred shots where only the motherboard was visible.
The first image in this post is when it was on its original case that was rusty.
It has these two heatsinks like you said, so those must be the voltage regulators.
So as long the module is 256kb and it has this pinout it is compatible, right?

Yes, that lokes like a linear VRM, two in fact - one for 3.3/3.52V, the other for split voltages down to 2.8V. The board should be able to supply 2.8V, so go right ahead with the P233MMX.

There is one more risk - it's possible the VRM (and indeed the whole board) isn't rated to deliver the current drawn by a P233MMX, particularly with a linear regulator (which draws the same current in 5V as it delivers in 2.8V, dissipating the difference as heat, hence the big sinks). The highest officially supported CPU in the manual is the P166. It draws 14.5W, which at 3.3V is 4.39A, and given the linear regulator it will also draw 4.39A at 5V. The P233MMX draws 17W at 2.8W, which doesn't sound too much worse, but due to the lower voltage, it represents 6.07A, which it will also draw at 5V on a regulator like this, so despite the CPU itself only using 17% more power, it represents 38% more load on the regulators and the board.

If you experience weird stability issues, clock the CPU down to 2x multiplier (133MHz) and see if they go away. If so, don't run it at such a high power draw anymore.

The revision C boards do have MMX support although they don't seems to mention anything beyond 200MHz, which is what I have in my rev CA board