Do you have a turbo switch hooked up? If not, try sticking a jumper on the header for it.

I tried it too (forgot to mention it) , if I jumper it down then the speed goes down (turbo = off) without changing the current L2 cache situation (it's off)

Could this be one of those cheap motherboards with fake onboard cache?

^ I thought of that and I tried another 256kb cache set from another mobo (untested but seems that it had it's cache upgraded from 128kb to 256kb - 4 chips are different set that the rest four and tag sram - who would upgrade fake chips?) , and still I got no results... both sram sets don't look fake or cheap in any way...

meh... today I tried erasing cmos, enabling/disabling various caching options, enabling/disabling autoconfig etc... nothing helped. Either I have 3 sets of fake 256kb cache chips or I am missing something obvious and embarrassing 🤣

I finally found why L2 was invisible on this mobo, turns out it was one damaged track 😀 it was connecting sram with the 74F245 , I rebuilt it and it works now 😁

Are you serious? How did you find this, that's quite an accomplishment 😀

nothing special really, noticed the fault and traced the points on the other side of the mobo... soldered a wire and it works! now it is time for an all-night memtest session 😁

allright! after ~17hrs of memtest things look good!

this is the temporary patch work to test the mobo:

and this is the final repair :