Any thoughts anyone?

Hi kolmio,

Well, an Am5x86-P75 should work on the Chaintech 4SPI board.

To test if the Am5x86 CPU is OK, be sure to check if there are no jumpers on JP24. This will put the Am5x86 in x3 mode and it should run at 100MHz on the 33MHz bus.
If you had an Intel DX4 or Enhanced Am486DX4 on this board before, there should be no jumpers change necessary for this test. However, if you were running the (non-WB) Am486DX4 NV8T, you need to check if the jumpers are set for the Intel DX4.

The 02/16/95-SiS-496-497/A/B-2A4IBC31-B2 BIOS is the latest for the 4SPI and supports the Enhanced Am486DX4 but not the Am5x86. That’s why testing in x3 mode gives you full BIOS support.

For further help, please let us know how the jumpers are set and which BIOS version you have.

Jan

Hi Jan, thank you

Chkcpu wrote on 2022-01-28, 15:12:

However, if you were running the (non-WB) Am486DX4 NV8T, you need to check if the jumpers are set for the Intel DX4.

I indeed had NV8T. But I understand that P75 supports both write-back and write-through mode, or not?

Anyway, I set the jumpers for WB mode and the CPU started fine 😀 so it's working 😀
And, by the way, I actually have 486SPM motherboard, not 4SPI 😁
Now I have to figure out how to set multiplier for 4x. But as motherboard is another one that is probably worth another thread.

Yes, the Am5x86-P75 supports both the Write-Through and Write-Back mode for its L1 cache. But often the Write-Back mode gives boot problems when the BIOS doesn’t know the Am5x86. That’s why I recommended to set the jumpers to DX4, so the Am5x86 runs in x3 and WT mode.

This should always work if the board supports the 3.3V DX4 and is a nice first step to find-out if the boot problem is in the board, the CPU, or the BIOS.

Okay, you have the Chaintech 4SPM, a great 486 PCI board. 😀
There are different version of this board, do you know which one you have (3, 5.1, 5.2 / M104)?

Also note the BIOS-ID as displayed on the bottom of the first BIOS bootscreen, so we can help you further with jumper settings and BIOS support.

Jan

kolmio wrote on 2022-01-28, 15:44:

Hi Jan, thank you […]
Show full quote

Hi Jan, thank you

Chkcpu wrote on 2022-01-28, 15:12:

However, if you were running the (non-WB) Am486DX4 NV8T, you need to check if the jumpers are set for the Intel DX4.

I indeed had NV8T. But I understand that P75 supports both write-back and write-through mode, or not?

Anyway, I set the jumpers for WB mode and the CPU started fine 😀 so it's working 😀
And, by the way, I actually have 486SPM motherboard, not 4SPI 😁
Now I have to figure out how to set multiplier for 4x. But as motherboard is another one that is probably worth another thread.

Well, the Am486DX4 (N)V8T has same jumper setting like a DX2 but 3,3 Volt and is a write through processor.
The Am486DX4 SV8B is completely different jumpered because it benefits from write back.

Chkcpu wrote on 2022-01-28, 19:16:

Okay, you have the Chaintech 4SPM, a great 486 PCI board. 😀
There are different version of this board, do you know which one you have (3, 5.1, 5.2 / M104)?

Also note the BIOS-ID as displayed on the bottom of the first BIOS bootscreen, so we can help you further with jumper settings and BIOS support.

Hi Jan,

so it's 486SPM M102.A
BIOS 02/17/95-SiS-496-497/A/B-2A4IBC32-B2

I used advice from https://pcrebuilding.altervista.org/49/128/2n … P75+133MHz.html and now BIOS recognizes this CPU as DX4 at 120 MHz
And from the test I understand that it actually runs at 133 MHz.

Hi kolmio,
Nice that you have the Am5x86-133 running now on your CH 486SPM.

Note that there is a 03/20/95-SiS-496-497/A/B-2A4IBC32-B3 BIOS available on https://www.ultimateretro.net/nl/motherboards/1208, but this B3 version is only 1 month younger than your B2 BIOS and has the same CPU support.
So no need to upgrade your BIOS. 😉

Cheers, Jan