Subj : Commodore Pet keyboard repair
To   : All
From : James Harris
Date : Wed Jan 10 2018 17:17:01

To my surprise, I find I have a Pet which works - all apart from the
keyboard, that is. So I have a query about fixing it.

So far, I have removed the keyboard and found that the PCB contacts work
if shorted with something conductive. Therefore the problem is with the
little black pads that a keystroke presses against the PCB. I have tried
these things:

* cleaning with isopropyl alcohol
* cleaning with contact cleaner
* abrading with a pen eraser

The latter was not really effective as there is too much give in the
part of the key which supports the pad so I would say that the operation
failed to abrade the pad successfully.

Where I am now is that a few pads work but most do not. I have tried
putting two meter test prods on the pads to measure resistance and found
that some only become conducive with significant pressure. I guess that
the rubber of some of them has become too hard with age.

So what can I do to fix them? Any ideas?


One idea I've had so far is to apply some conductive matter to the pads.
I have tried a product called Keypad Fix on a remote but found it dries
to be too inflexible and crumbles on use, albeit that that was on larger
contacts.

Another option is conductive paint such as

https://uk.rs-online.com/web/p/solder-pastes/8352699/

A further option is to cut tiny copper-film discs and stick them to the
existing pads.

Any of those good options? Other suggestions welcome.


--
James Harris

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