To my overview page

This page will contain stuff about repair of old computers (presently only the first but hopefully I will get around to write more on this subject).

Keyboard keyswitch cleaning

Bad keys are such an annoyance, and replacement keyswitches are hard to come by nowadays. So I clean them, inside.

Lots of work but, wow it's a great success.

1 Open the machine and unscrew the screws holding the keyboard.
2 Take away the caps from the key and several of those around it, carefully prying them straight up.
3 Desolder the switch so that the leads move freely in the holes (sideways).
loose keyswitch in frame4 It is now only the catches that hold it in the metal frame and they can be carefully bent inwards so that they release and the switch so that it comes out upwards.

Photo from my model 4, desoldered and with catches loosened.
keyswitch out5 Having it out, release the 4 catches around and take the switch apart (carefully, observing how the pieces should go together again)
keyswitch openPhotos prying open the catches and half apart
6 With the thing apart I clean the metal pieces, the actually switching parts, with contact cleaner spray and q-tip. If there is a membrane cup thing I'd clean that too but more carefully and not pressing hard.

Photo of the parts. I would clean the bottom two parts (to the right in the picture) with contact cleaner and rubbing with a q-tip, do the membrane thing very light and carefully, and the metal plates in the bottom with some force.
7 Reassemble and use a multimeter to see that the switch is ok before putting it in place and solder it again. (It is too much work if you have to get it out again).

The photos are of the keys in the TRS-80 Model 4. I have also done my Model III. It has different keyswitches, with a metal tongue instead of the membrane thing.

Disclaimer This is not easy, don't do it unless you are confident that you can succeed. Some skill with small things and soldering is needed, and to remembering how to put together again. If you do any of this you do it at your own risk.

©2005 Knut Roll-Lund
To my overview page