Could it be the PCI Latency issue? https://www.vogonsdrivers.com/getfile.php?fil … 6&menustate=0,0

I tried but unfortunately didn't fix it.

I could reproduce the issue in DOS, can we close/delete this thread and I will create a new one with more infos in the appropriate forum?

Run a memory test on the system.

Any program/distri you can recommend? I remember I never had any errors with memtest even after 24 hours

This sounds exactly like failing memory. I had this same issue.

schlang wrote on 2025-07-14, 14:04:

Any program/distri you can recommend? I remember I never had any errors with memtest even after 24 hours

I used some older version of MemTest86+ on my retro machines to test memory I bought on eBay.

schlang wrote on 2025-07-06, 23:36:

I tried but unfortunately didn't fix it.

Slow down memory and/or cache and see if the errors stop

I used BIOS failsafe defaults but with the same result.
Now I'm running memtest86, should I be using memtest86+?

Thats what I have after 2 hours of memtest

That appears to confirm bad RAM, or RAM being run past it's specs.

I made further tests and the CRC errors do not happen if I disable both Internal and External CPU Cache in BIOS

schlang wrote on 2025-07-14, 22:56:

I made further tests and the CRC errors do not happen if I disable both Internal and External CPU Cache in BIOS

And what happens if you disable one OR the other and test ?

I tried first with only external cache disabled and I had CRC errors. Do you suggest it would make sense to try internal disabled and external enabled?

Memtest86 throws errors on test #5 with cache enabled, looks very reproducable

schlang wrote on Yesterday, 10:23:

I tried first with only external cache disabled and I had CRC errors. Do you suggest it would make sense to try internal disabled and external enabled?

If you can reproduce the issue with only one of the caches disabled, it would strongly suggest that the fault lies with that cache.

Keep in mind that the K6-iii+ has on-board L1 and L2 cache AND yout motherboard's installed L2 cache, if any, effectively becomes L3 cache, AFAICR.

I don' have any personal experience with that CPU, but I suspect that your BIOS option for L2 cache actually enables/disables only the motherboard cache while BIOS option for L1 cache actually enables/disables BOTH the L1 AND L2 on-CPU caches. This can probably be validated through the CTCM cache check utility and/or K6-3 specific utilities.

That being said, if the system used to run reliably and now doesn't, it suggests a hardware fault with either the CPU itself, the motherboard cache or the motherboard itself being the most likely culprits (in descending order), IMHO. The PSU, in this case, seems like an unlikely candidate, but stranger things have happened.

Another thing look into is whether any specific BIOS settings might be required for this setup to run reliably might no longer be set due to a CMOS clear. I am just speculating on this one.

Also it was correctly suggested earlier to relax the cache timing but there was no feedback on this, or whether such BIOS options exist at all.

I use BIOS Fail Safe defaults, no aggressive timings.

I switched out the mainboard and the errors are gone, I assume we can rule out CPU and memory which leaves the board as the culprit.

Is it time to throw the board away or can it be salvaged?

schlang wrote on Yesterday, 13:35:

I use BIOS Fail Safe defaults, no aggressive timings.

I switched out the mainboard and the errors are gone, I assume we can rule out CPU and memory which leaves the board as the culprit.

Is it time to throw the board away or can it be salvaged?

Has the board ever had its capacitors replaced ?