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Re: Notes on Cleaning and Repairing an Apple II Plus

Linards Ticmanis wrote:

On 04/25/2011 11:22 PM, Michael J. Mahon wrote:



Once you spray or wash something into a keyswitch, any non-volatile
components (including dissolved dirt) will stay there forever--unless
you enjoy disassembling keyswitches and manually cleaning them.  ;-)



Which isn't all that hard with the black-and-gray switch type Apple or
their keyboard supplier seem to have used most commonly. Just unsolder
the problematic switch, remove the caps of the surrounding keys, press
the snap-in thingies towards the center and carefully pull it out
(upwards). Then it's easy to take it apart, it's all just snapped
together, no screws, no glues.


Each switch is not too bad, but a few dozen is a real grind.  ;-)


                                As long as you remember where each part
goes and take care that the spring doesn't propel itself away, you can
then get a small screwdriver or something similar between the two actual
contacts and carefully scratch a bit, then reverse the whole process.
That way I recently revived some switches which simply weren't willing
to work right - I'd get either no character on screen or several at
once, no matter how many hundreds of times I had pressed the key. Turns
out the culprit was a bit of verdigris which had formed on the contacts,
probably too much of it to be removed without disassembly.


This kind of "direct intervention" is certainly effective, but there
is a danger that it will accelerate future failures.

The switch contacts are typically phosphor bronze (for springiness)
plated with silver (for low contact resistance) and sometimes "flashed"
with a thin plating of rhodium or other corrosion-resistant metal.  The
contacts are then lubricated with a dry, non-corroding lubricant for
longer life.

Scratching or sanding the contacts removes the plating(s), exposing
the base contact metal.  This will certainly work, especially if the
switch is used regularly so that the wiping action of the contacts keeps
them oxide-free.  But it also makes the contact more vulnerable to
oxidation.

If necessary, contacts should be burnished lightly with a silver
polishing cloth or a thin wood shaving.  The mild abrasion will remove
tarnish from the silver plating while leaving it (hopefully) intact.

In the case of your green-corroded contact, the silver was clearly
already breached, since the green coloration indicates the presence
of copper salts from the bronze.  This is usually the result of some
prolonged exposure to moisture.  Hopefully, it indicates that only one
keyswitch was affected, but maybe not.

A keyboard with several corroded switch contacts is a pretty good sign
that a new keyboard is in your future.

-michael

NadaNet 3.1 for Apple II parallel computing!
Home page:  http://home.comcast.net/~mjmahon/

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