Restoring rubber keyboard on a logic analyzer

[dwight]

Just out of curiosity, you might try a little extra fine sand paper on the button. You have little to loose as it doesn't work anyway.

Dwight



________________________________
From: cctech <cctech-bounces at classiccmp.org> on behalf of shadoooo via cctech <cctech at classiccmp.org>
Sent: Thursday, April 26, 2018 12:09:49 PM
To: cctech at classiccmp.org
Subject: Re: Restoring rubber keyboard on a logic analyzer

Hello,
this kind of keyboards was made using small pieces of conductive rubber to
close the circuit designed on the PCB.
The rubber was an uniform compound, so even with severe usage, i.e. high
consumption, the conductivity remained constant.
However, in more recent / cheaper products, the rubber is the same for the
whole keyboard, i.e. simple insulating silicone rubber.
The conductive surface is only painted over the silicone.
No doubt it comes away faster...
In this case, cleaning with alcohol just removes the remaining paint,
referring the keyboard useless.

The solution is simple: cover the key contacts with something conductive.
I know that conductive paint is sold somewhere, but it's pricey and don't
think it would last much...
The cheapo solution is to cut small pieces of aluminum foil, and glue it to
the rubber.
Given that the keyboard is almost always made by silicone, I always use
silicone glue to assure the sickness.
Be careful to put a very thin layer of it only over the center of the foil,
then put it in place and press a bit around with the fingertip to let it
take the shape of the contract.
Too much silicone would come out when pressed and would cover the graphite
on the PCB.
This method worked well with several TV remote controls.
I could suggest you to try with one key,
then let the silicone to dry before remounting the keyboard, then check the
result and eventually repeat on other keys.

Andrea