Nearly all Model M keyboards have horrendous key rollover issues, supporting as little as 2-key rollover and only between certain sets of keys; within a set, the keyboard will only register one keypress or the keyboard will generate garbage keypresses.
The microcontroller they had been stuck on for ages became unavailable so they started producing models with Rpi2040's, which can run QMK. If you still have it kicking around, maybe it is one of the QMK supported keyboards or they've released a fixed firmware for it?
Unfortunately the Model M and derivatives have long been eclipsed by the market. Better electronics/firmware, mechanical switches with choices in travel, force, noise level, and tactile feel... designs with lower profiles, different grid arrangement and almost every key count/layout imaginable...
Interesting, thanks for the link. I'll investigate and see if I can get it working more better.
But FWIW, I have multiple Model M classic keyboards (from 1992), and also other Unicomp full-size keyboards, and I've never had this issue with them.
I also know the story that the market has "better" options than the Model M. Maybe it's just nostalgia but I've never found anything with the same feel as a buckling spring. The Model M just feels nice to me.
For my Model Ms I've ordered and soldered PCBs from an open source project that are drop in replacements for their controller PCBs and convert them to USB A plus QMK firmware. (I'm going a bit by memory, as I had to stop the project for a while and still have to switch a couple of them, but can look that for you if you're interested)
It sounds like Unicomp designed the newer keyboards to have better PCB designs, but had firmware issues with key rollover on the mini (is that yours?) and may have fixed it: https://www.reddit.com/r/modelm/comments/13o0jkr/raspberry_p...
The microcontroller they had been stuck on for ages became unavailable so they started producing models with Rpi2040's, which can run QMK. If you still have it kicking around, maybe it is one of the QMK supported keyboards or they've released a fixed firmware for it?
Unfortunately the Model M and derivatives have long been eclipsed by the market. Better electronics/firmware, mechanical switches with choices in travel, force, noise level, and tactile feel... designs with lower profiles, different grid arrangement and almost every key count/layout imaginable...