Apples aren't the only fruit.

[rubber_jonnie]

That tape is quite a low resistance. We use it at work for boiler lagging.

What about conductive painting the surfaces?

It is extremely low resistance, you're right, and having read the latest posts it wouldn't be suitable as it'd likely just short the contacts.

Interesting subject though. Would it be feasible to use the old foil discs, or are they too far gone?

[stephen_usher]

That tape is quite a low resistance. We use it at work for boiler lagging.

What about conductive painting the surfaces?

It is extremely low resistance, you're right, and having read the latest posts it wouldn't be suitable as it'd likely just short the contacts.

Interesting subject though. Would it be feasible to use the old foil discs, or are they too far gone?

The decomposing PVC foam has released chlorine which has attacked the aluminium coating on the back of the mylar. If this hadn't happened then irrespective of the foam degradation the keys would still work.

The emergency thermal blanket material is identical to the original disc material, so you just need to cut out disc of that and stick it to some foam (with the aluminium coating away from the PCB). It's the foam which is proving to be the trickiest item to source.

I should have some 3mm thick, 12mm wide weather proofing foam with adhesive on both sides arriving this afternoon and I can cut discs from that using the 11mm hollow punch I've obtained.

[rubber_jonnie]

It is extremely low resistance, you're right, and having read the latest posts it wouldn't be suitable as it'd likely just short the contacts.

Interesting subject though. Would it be feasible to use the old foil discs, or are they too far gone?

The decomposing PVC foam has released chlorine which has attacked the aluminium coating on the back of the mylar. If this hadn't happened then irrespective of the foam degradation the keys would still work.

The emergency thermal blanket material is identical to the original disc material, so you just need to cut out disc of that and stick it to some foam (with the aluminium coating away from the PCB). It's the foam which is proving to be the trickiest item to source.

I should have some 3mm thick, 12mm wide weather proofing foam with adhesive on both sides arriving this afternoon and I can cut discs from that using the 11mm hollow punch I've obtained.

Interesting stuff, looking forward to seeing your results.

[stephen_usher]

Interesting stuff, looking forward to seeing your results.

What I may try doing is sticking a strip of mylar on top of the foam strip and then punching the disc out as a single unit rather than doing them individually and sticking them together afterward.

[PhilC]

I admire your commitment to getting these old computers fixed Stephen. Apricon certainly did come up with some interesting technology back in the day.

[rubber_jonnie]

Interesting stuff, looking forward to seeing your results.

What I may try doing is sticking a strip of mylar on top of the foam strip and then punching the disc out as a single unit rather than doing them individually and sticking them together afterward.

Sounds like a good thing to try.

[stephen_usher]

I admire your commitment to getting these old computers fixed Stephen. Apricon certainly did come up with some interesting technology back in the day.

Of course these capacitative pads aren't just used by Apricot, Apple Lisas have the same. So if I work out an easy way to produce them then that benefits the whole community.

[stephen_usher]

The new foam has arrived, but it's only adhesive on one side. Otherwise it's working fine. I just have to use PVA on the mylar side, which isn't a huge issue.

Top tip: Mark the side of the mylar which is conductive with a sharpie so that you can tell which way up the discs need to be on the foam. :-)

[stephen_usher]

OK, that foam is a bit too thin and too stiff.

The problem is that I have no way of telling the type of foam I'll be getting before it arrives.

[stephen_usher]

One more throw of the dice. Self adhesive acoustic foam this time.