HP-67 bouncing keys

[Geoff Quickfall]

Just to be clear, de-oxit red removes oxides and is still active if left on the electronics.

This is a process for stubborn key bounces.

I only do this if the soap solution, followed by water rinse, followed by IPA (99%) rinse and thorough drying, application of de-oxit gold does not resolve the bounce AND if no sulphate (blue) corrosion is present. And of course cut a new plastic spill sheet using the original as a template.

Remove the keyboard PCA. note: AT ALL TIMES KEEP THE LED BLOCK CLEAR OF ANY SOLUTIONS.

Wash it with a degreaser soap solution using an artist brush all while keeping the LED block dry.

Then I submerge the keyboard in a mild, luke warm vinegar solution especially if there is evidence of corrosion. Keep the LED block away from the solution.

Next I cut the 1500 / 2000 grit sandpaper into strips that slip between the keyboard contacts. Draw the sand paper through while applying light pressure to the top of the ‘dome’.

Rinse with IPA to remove particulate matter from the light sanding.

Apply de-oxit red with brush or by coating standard printer paper cut into strips to remove any pitted oxidation not removed by the sanding. Allow to sit for awhile.

Rinse with IPA

Apply de-oxit gold and test.

Repeat if necessary.



Yes, gold is a preservative, not an oxidant remover. I have applied de-oxit red to contacts in radio equipment and left it there. Come back in a year and unusually the contacts have corroded. This is anecdotal but makes sense as the de-oxit red has an active de-oxidant which continues to work after the oxidation is removed. Now I let it do its job then clean it off and apply the gold in its place.

Cheers,
Geoff

As a side note, only do this if cleaning the keyboard PCA with soap solution does not rectify the problem. Again do as little harm to the electronics as possible.


Both teenix and GreyUser have excellent points:

Once IPA is used I apply the deoxit gold to the PCA coating the entire board.

If you have access to an ultrasonic cleaner (they are cheap) use it. However, I have seen thick blue sulphates emanating from the contacts. The use of a fibre glass pen, dental picks and the sandpaper may speed up the process.