TLC Ideas for LA120 Keyboard?

From: Andreas Freiherr <>
Date: Mon Feb 17 07:50:00 2003


the contacts you describe from your LA120 (cannot look at my own right
now) seem to be similar to what I saw in a VT100 keyboard. This keyboard
had been stored in a place were mice and rabbits lived, but it recovered
from initial contact problems just by continued use: the isolating
plastic has a cleaning effect on the electrical contacts as it slides
between them.

In general, I often have success when cleaning contacts by wiping them
with paper: it's rough enough to remove corrosive layers, but soft
enough to keep the contacts intact, and it's readily available. Best way
to apply is: put paper between contact fingers while the switch is open,
then close switch, and, while applying little or no additional pressure
on the contacts, move paper back and forth a bit.

You will sometimes see a line left on the paper, especially if the
contacts are very dirty. This line proves that the method works.

Given the limited space around your keyboard contacts, you'll probably
want to cut a narrow stripe of paper, insert it with the help of a
screwdriver because you cannot open the contacts otherwise, then take
out the screwdriver and just pull out the paper from under the contact.

For this type of mechanical contact, a chemical solvent may also be
appropriate. I don't use contact cleaners on variable resistors (and
some other stuff) because it solves the problem only for a limited time,
and when the problem reappears afterwards, it's worse than before. A
"volume" potentiometer treated this way will crackle even louder in
about a month or two.

BTW: nice ASCII graphics! :-)


Jeffrey Sharp wrote:
> Well, my DEC LA120 is almost perfectly operational. Its only problem is a
> set of keys that do not work when pressed. I'd like to fix that.
> Any suggestions?

Andreas Freiherr
Vishay Semiconductor GmbH, Heilbronn, Germany
Received on Mon Feb 17 2003 - 07:50:00 GMT

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:35:55 BST