Not sure if it would make a difference, but it might.

Do you have L2 cache installed?
I couldn't get WB cache for the CPU working in my 486 build until I installed some L2 cache, then it worked fine.
Sounds strange, but these old motherboards can be very picky.

I have 256 kB of L2 cache installed so that shouldn't be a problem. It's a nice board but I have a hard time figure some things out, even with a manual. I.e. to this day I don't know how to enable 133MHz on the AMD CPU. I tried to set the jumpers to 486 DX2 mode without success, then I tried to reconfigure jumper settings one at a time and everything I have managed to do was to set the CPU to 120 MHz. Unfortunately I have yet to buy a multimeter which would be quite handy in this situation.

Is the L2 cache set to WB or WT?

I made some tests some time ago and came to the result that you get best speed if only one of the caches uses WB. So if the L2 cache is already WB, leave the L1 cache at WT - this will give you better speed.

That's odd, MB should post regardless how the CPU cache writing policy is set, maybe that jumper which causes your MB not to POST is responsible for a completely different setting? Remove CPU from the socket and with a multimeter, in continuity mode, try to trace to which CPU socket pin that jumper connects.

I'll probably need a multimeter to solve this mystery. The L2 cache in WB mode does produce different results, mainly positive, but there are a few instances when the PC is slower (i.e. Doom). What is better - to set L1 to WB or L2 to WB?

Paar wrote:

If set the jumper on the system boots fine but I'm stuck with WT cache (according to CHCKCPU tool) even though I set L1 cache to WB in BIOS.

Check if you have set the TURBO jumper correctly

Paar wrote:

I'll probably need a multimeter to solve this mystery. The L2 cache in WB mode does produce different results, mainly positive, but there are a few instances when the PC is slower (i.e. Doom). What is better - to set L1 to WB or L2 to WB?

From the four possible combinations, I've got best speed when L1 is WB and L2 is WT. Posted some info on this here:

AMD 5x86 X5-133 (now with POD)

If you can't get L1 to work in WB mode, set L1 to WT and L2 to WB.

sonicx wrote:

Check if you have set the TURBO jumper correctly

AFAIK there are only TURBO jumpers for TURBO switch and TURBO LED. Both are ok, at least TURBO works when using L1 in WT mode. The FSB is lowered to 15 MHz when active so the CPU's speed is ultimately 45 MHz.

derSammler wrote:

From the four possible combinations, I've got best speed when L1 is WB and L2 is WT. Posted some info on this here:

AMD 5x86 X5-133 (now with POD)

If you can't get L1 to work in WB mode, set L1 to WT and L2 to WB.

So far I'm stuck with the latter option.