Also try testing memory with memtest86 or similar.

Yes, forgot to mention that booting with F5 and running PCTools SysInfo, it passed all the memory tests 😒

Just came across two documents back from '92 with explanations and step-by-step troubleshooting, thought it would be useful to post the links here for other people with similar problems. Will try the steps described in #232 myself tomorrow, hopefully to at least pinpoint the cause, if not solve it altogether.

Quarterdeck Technical Note #142 - QEMM-386: Exception #13 Explained
Quarterdeck Technical Note #232 - Exception #13 Advanced Troubleshooting

My old 486DX2-66 used to do this all the time. Coincidentally I also had a CL-GD5426 video card (mine was ISA), but I never suspected it as a factor. My symptoms were more severe than yours sound though. Have you tried running any DOS games that stress this machine, or has it just been Windows?

For me, some of the more intense DOS games were prone to freeze, and it happened whether QEMM was running or not. QEMM just added an error message similar to what you posted. I had problems with pretty much any DOS game that used an SVGA mode, but VGA was mixed. One game that crashed very quickly was Ultima 7, and I think the DOS version of SimCity 2000 was the same way. DOOM was stable.

Windows 3.1 was usually stable but it would sometimes give error messages - I don't remember what they said. Attempting to run at higher res/color video modes would make it much less stable.
It was never solved, but I wasn't very good with computers back then. I think my motherboard (cheap PCChips board) was having memory errors when it was under stress. I played with every jumper and BIOS setting but I didn't really know what I was doing. The only thing that seemed to help was disabling caches, but that wasn't tolerable.
If I could do it again now, I'd try running at 25MHz bus, make sure the clock ratios are set correctly, try higher wait states, and measure operating voltages.

If you're having no stability problems outside of getting that error when you exit Windows, then your situation is different than mine was.

Bad caps are always a possibility, especially for a board this age, but that's just a guess.

psychz wrote:

Yes, forgot to mention that booting with F5 and running PCTools SysInfo, it passed all the memory tests 😒

I don't know how good that test is, but I wouldn't put much faith in it. I think most memory tests back then were too simplistic to detect many faults. Memtest86 has definitely proven to be an effective memory test and a long multi-pass run of it (overnight or so) would be more convincing IMO.
If it passes memtest86, then I'd also try a torture test of Prime95/mprime, if some build of it exists that can run on a 486.
If it's really a software problem, then I don't have any ideas.

Perhaps it isn't the same issue since I only get this behavior when I do have some memory manager enabled, but to be honest, I haven't really stressed the board to check its stability. I used PCTools SI only because the latest floppy image of memtest86 would just reboot and I couldn't be bothered to search for an older version hehe 😜 Doom 1 and One Must Fall 2097 seem to work fine however, and so do Windows 3.11 at 800x600/65k colors. The caps don't appear to be bad, however, truth is you can never be 100% sure with such old hardware. Will have a go metering the PSU as well. Oh well, lots of things to check today I guess!

There are some old DOS versions of Memtest. Boot bare system (F5) and run the exe file.

http://www.memtest.org/download/4.10/memtest86+-4.10.exe.zip

mt86+ v4.10 won't work; v2.00 reports no problems. Quarterdeck's technical notes didn't help much as well. Feel like giving up on this one...

- also check the BIOS settings. Put everything to Default and slowest timings
- try without a sound card
- put sound card in another SLOT
- put VLB VGA card in another SLOT

Do you have VLB or ISA I/O controller? If VLB try swapping it with VGA and so on... Something should work in the end 😉