Troubleshooting a weird keyboard on a Pentium III

Clara and I found this Pentium III motherboard and a collection of parts off the side of the road in Chatswood back in 2024. I put it into an Antec case from my father in law, and it’s gradually become my primary utility PC. I use it to test hard drives and expansion cards before I put them into my other machines, and I use its 5.25 and 3.5 disk drives for imaging and creating boot disks. Weirdly, about a month ago the attached PS/2 started sending errant signals. Or so I thought. I’d be in a utility checking the status of a drive, like a gentleman, when suddenly I’d be scrolled a page further down, or a random menu item would be selected. If an invalid key was “pressed”, the PC speaker would chirp indignantly. One morning I woke up to hear the PC speaker beeping on and off nearly continuously, as though a ghost cat had sat on the keyboard, or Ed Sheeran was giving a concert. Worried that it might somehow be an electrical issue on the port, I connected a USB keyboard instead. Alas,…