Part of the upper video memory is most likely bad. I have a notebook with almost the same issues. It works in most cases, unless a game or a tool uses the part of the video memory that is bad. Text mode is also messed up when exiting from Mode X (e.g. DOOM) or when all text pages are used.

Using modetest.exe, it was quite easy to determine the culprit.

Thanks for the tip. This is all pretty alien to me though - never had to faff around with memory areas.

modetest.exe shows mode 5c, 5d, 5d and 5f all have an error at character 1. These are mainly 256 modes.

What do I do with this information, though?

EDIT: I ordered a seperate ISA Cirrus Logic card of a slightly older model but with the same amount of memory just in case. I can use it as a spare card in tests anyway.

You could simply swap the video RAM chips. Should be pretty easy if you can solder.

derSammler wrote:

You could simply swap the video RAM chips. Should be pretty easy if you can solder.

I'm very very reluctant to mess with this motherboard. The replacement card should be a good start - I will do a benchmark to make sure I don't lose too much performance and if it removes my problems, yay.

OK update - my Cirrus Logic card arrived. I did a few tests and the games with the garbled text are fine now BUT the two games (Blues Brothers & Krusty's Fun House) both have messed up tiles still so it seems it's not related to the graphics card. My old IBMs all had Cirrus Logic chips and played those games fine.

When exiting Blues Brothers, I get the following error though: "memory allocation error". I wonder if the problem is perhaps something to do with regular memory. Not the RAM sticks themselves (I'd have far worse problems than that if they were faulty) but the memory manager?

OK update!!!

Me being me, I refused to give up. The Cirrus Logic card was crap - it made my FPS drop massively so it was not an option. I saw a slightly newer model of the same PC on sale in great condition, snapped it up, moved the drive over and the sound card and ..... I got the exact same errors in the exact same games. The newer model doesn't have the same Cirrus Logic chip either (Cirrus Logic 5436 instead of the 5430).

So I did a fresh install, did everything from zero and nothing changed. So I did some Googling, looked for specific games that had the problem and ... found a small tool called TSRFONT. Apparently, this tool fixes a kind of compatibility issue with certain Cirrus Logic cards. Basically, nothing was really wrong except that a certain font gets corrupted. Using this tool fixes the problem. I'm posting this here in case someone else has this same problem.