Broken Amiga keyboard

Most keyboards I know of one exception [1]) have the keyswithcs arranged in a rectangualr matrix. The 'column' lines are scanned (each one is driven in turn), and the row lines are tested by the keyboard cotnrolelr to see if any swithces are closed [1] The kleyboard for the hP9816. In gneral,. individual keys that have failed mean a problem with those swithces. A comlete row or column of the matrixx not working oftne indicates a problem with the logic circuitry associateds with that row or column. Now 4 rows is rather too few (8 is more common), so perhaps an eitrie column isn't missning. but of course you don't have to ahve a swithc at every possiton. Perhaps the matrix is electrically 16*8, giving places for 128 keys, but only, say 101 are used. That could result in a column with only 4 switches in it. Needless t osay a schematic, including a matrix layout, is very useufl, but I assume you don't ahve one, and have no chance of getting it. Do you know how thw keyboard works mechanically, If there are individual keyswitchs solder to the PCB, you can use an ohmmeter to test each switch and see if it closes in the obviosu way. You can also trace the PCB tracks between the switchs and back to the control electronics to see if there are any breaks. If you can identify what drives the columns (it may an putput poert on a microcontrolelr, or a separate TTL decoder IC to save pins on the microcontrolelr), you can see if each column is being driven using a 'scope or logic analyuser. If it's a membrane keyboard, identfuable by flexible plastic 'tails' with conductive traces on them plugged into sockets on the control pCB, then first make sure those are seated properly. Some mambrane assemblies are held together by lots of small screws, others are heat-staked. If the former, you could caefully take it apart (make a diagram of where the keys go, jsut in case things come loose), and inspect the membrane sheets. Maybe the defective keys need cleaning, maybe there's a break in one of the traces (the _condcutive_ silver paint sold for repairing traces, etc is useful for reparing this. If it's a Keytronics capacitive unit, identified by the PCB under hte keys with apparanetly nothing soldered to it in that area, remove the PCB by taking out all the scresws. You can now inspect the foam/mylar pad assemblies. Perhaps you have some decayed foma, or the meralisation ahs disappearsd from the faulty keys. -tony