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I've got a reasonably large collection of old computers that I've mostly picked up at such things as car boot sales, etc., before I went to University. Now that I'm working, I'm starting to look at some of the projects that I never finished back then.

The main project is the repair of the keyboard for the Apricot Xi. I stopped on this simply because I had no idea how to proceed (I unfortunately also managed to lose the bolt for the voltage regulator heatsink but I should be able to replace that without too much difficulty, and I think I still have all the important parts). The construction of the keyboard is not like I've seen in the past, and it's very proprietary and unusual so it's not something that could easily be replaced wholesale.

The PCB has pads for each key as you'd expect to find in a modern keyboard. However, instead of rubber dome switches, the bottom of each key has a piece of green sponge on it, many of which have lost their sponginess or become brittle with age. On the bottom of each sponge is a small plastic disc coated with some silvery conductive material. There are three problems:

  1. Contacts on the PCB are dirty and corroded (easy to fix I assume with contact cleaner)
  2. Sponge is less spongy than it should be (perhaps cutting new pieces of sponge is feasible, if I can figure out how to attach them properly?)
  3. Conductive material has rubbed off many of the plastic discs

It is #3 that I really don't know how to sort out. Can you buy conductive plastic discs which you can glue to sponge? Is it possible to "repaint" the discs with conductive paint of some sort?

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  • There are various sorts of conductive paint, often silver based, e.g. here (sorry, German Amazon). That's great to repair PCB boards, but I've no idea how well it will hold up if it's mechanically stressed in some way. I don't know how the discs look like, maybe it's possible to replace them with discs completely made out of metal? Machining metal discs of known diameter should be possible somewhere if you ask around.
    – dirkt
    Dec 15, 2016 at 12:17

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When I patched up my Xi keyboard, I used double-sided adhesive pads cut to the right size, with aluminium foil tape to replace any missing discs.

These days it's also possible to buy replacement foam pads -- disintegrating foam is a problem common in KeyTronic keyboards, and searching for 'KeyTronic foam' on eBay finds a seller of replacements.

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