A colleague of mine, is trying to repair his mid-1970's keyboard. He may well find old-stock unused keyswitches, but I'm betting not. They were likely made by MicroSwitch, owned at some point by Honeywell. They are Hall-effect. They have four pins, they need 5V power. This is not a common microcomputer. Here's a link to deskthority.net, of what the keyswitches look like. https://deskthority.net/wiki/Micro_Switch_SD_Series But there's lots of variations. No point in describing them further, most won't have these keyswitches. If you have something like this, and can unsolder several (and one for inspection), contact me directly and we'll go from there. Herb Johnson -- Herbert R. Johnson, New Jersey USA http://www.retrotechnology.com OR .net