@mwichary Four LEDs, including “S2” which is one of the red keys on the left.
PS2 to USB interfaces simply can’t cope with the custom PS2 codes produced by the nonstandard keys, resulting in ghosting, persistent held keys and other horrors. I could drag out one of my old machines with a PS2 interface and write a driver, but to what end?
The plan is to replace the PIC with a Pi or equivalent and do a proper USB interface. It’s a good plan and has been for years! One day, one day.