Restoring rubber keyboard on a logic analyzer

Peter Coghlan cctalk at
Wed Apr 25 16:16:33 CDT 2018

> I have a Philips logic analyzer (PM3585) which is about 20 years old at this point.  It seems to be basically functional except for the keyboard, which unfortunately is a critical part.
> This is one of those molded rubber type, with a circuit board behind the rubber that has contact areas made of carbon film (at least they are black in color) and on the back of each key a small cylindrical bump also coated with carbon. Some of the buttons work but most don't seem to even if I press hard.
> I've disassembled the keyboard, which was easy enough.  Inspection shows no damage and no signs of corrosion or contamination.  I wiped everything with isopropyl alcohol anyway.  The result is no change in behavior.
> Any suggestions for what to do next?

I had a similar problem with an old VCR remote control.  The problem seemed
to be that the bumps on the back of the keys lost their conductivity (and
cleaning them made them worse).

My solution was to glue pieces of aluminium foil to the back of the keys.
It was tedious but it seemed to sort it out.

Peter Coghlan.


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