fsinan wrote on 2024-02-07, 09:32:

Will try the Cyrix 5x86-100GP on it but could not found any manual for this board. Anybody out there have a source of info?

https://theretroweb.com/motherboards/s/u-board-jk-042e

First I would start testing, if everything works as expected with the Amd X5-133, so 133MHz and to verify if the L1 is working in WB mode.
Second, then it would be good, when you provide better pictures of the board, the ones on retroweb are hard to read. So somebody can upload it to retroweb then.

Changing the CPU to Cx5x86 should be the last step.
If 1) was successful, you need just to replace the CPU. It will probably then run correctly, but only at 66MHz, because the AM5x86 interprets the 2x jumper as 4x. So to run the Cyrix at 100MHz only one jumper has to be removed.

Do you actually have this board in your hands, or was this more a theorectical thread/question?

That board looks pretty much identical to this one which does have a jumper manual:
https://theretroweb.com/motherboards/9881
As far as I can see it's exactly the same design, just a different colour PCB and here and there different passive components. The actives all look the same though and every jumper I can read on the pic for your board seems to correspond.

Bad news is that despite offering settings for a bewildering array of CPUs, it doesn't document what every jumper actually does. So I hope the "CS5X86" works for you. I would recommend noting current jumper positions as there is no "AM5X86" setting listed. I suspect it would be the one for "(SL)AM486DX4", as that's the most likely one for 486DX4 with WB cache (and the 5x86 is really just a 486DX4 with extra multiplier added) - but at the very least the multiplier jumper will be different, whichever one that is.

dionb wrote on 2024-02-07, 11:08:

That board looks pretty much identical to this one which does have a jumper manual: https://theretroweb.com/motherboards/9881 As […]
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That board looks pretty much identical to this one which does have a jumper manual:
https://theretroweb.com/motherboards/9881
As far as I can see it's exactly the same design, just a different colour PCB and here and there different passive components. The actives all look the same though and every jumper I can read on the pic for your board seems to correspond.

Bad news is that despite offering settings for a bewildering array of CPUs, it doesn't document what every jumper actually does. So I hope the "CS5X86" works for you. I would recommend noting current jumper positions as there is no "AM5X86" setting listed. I suspect it would be the one for "(SL)AM486DX4", as that's the most likely one for 486DX4 with WB cache (and the 5x86 is really just a 486DX4 with extra multiplier added) - but at the very least the multiplier jumper will be different, whichever one that is.

I have it with me and it is working as a system.

It seems problem solved. The retroweb listes 1.U-Board ST1A rev:B and 2.U-Board JK-042E

Mine has two names both on the board. Here are the picture of the board. And 1 has a jumper setting doc. I'll compare it with mine and inform you about it.

Sent this info to retroweb.

See the pics.

fsinan wrote on 2024-02-07, 14:27:

It seems problem solved. The retroweb listes 1.U-Board ST1A rev:B and 2.U-Board JK-042E […]
Show full quote

It seems problem solved. The retroweb listes 1.U-Board ST1A rev:B and 2.U-Board JK-042E

Mine has two names both on the board. Here are the picture of the board. And 1 has a jumper setting doc. I'll compare it with mine and inform you about it.

Sent this info to retroweb.

See the pics.

Good pictures!

Yes, settings work with the U-Board ST1A Manual.