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Hi;
I remember the days I was at the University (80's) when an HP29C was shown to me as having this sort of problem. I opened the keyboard and I saw the plastic domes for each key, as you mention. And the faulty key had a broken cooper trail, because in these keys, the cooper trails are slightly stretched when the key is pressed. The newer plastic dome-type keyboards have no trails, only a centered conductive island in the inner middle part of the dome.
If, at that time, I had the option to use cooper foil with conductive glue (available today) or the conductive inks, I'd try repairing the faulty key the way you mention: disassembling and applying the conductive material. And I think there are also other options.
Success!
Luiz (Brazil)
(P.S. - I'll be back... soon)
Edited: 23 Oct 2003, 10:51 p.m.
Posts: 234
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Joined: Jan 1970
Victor,
I have succesfully repaired woodstock keyboards , plastic dome types.
Two methods:
1. Using conductive ink. It is a graphite based ink, and after dry it becomes a very dark grey. This method is good if the plastic dome is not damaged.
2. Using a 12C metal dome. I cut away one metal dome from a deceased 12c, and successfuly used it in place of a damaged plastic dome. The damaged key was "enter", and the holes is the 12c metal dome matched the plastic pins in the woodstock keyboard.
Good luck,
Renato
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Most likely the problem is a bad contact under the key dome. You fix these just like the ones with the access hole under the keys, except that you must drill your own hole with a small hand drill. Be careful not to drill through the etches on the other side. This can be a problem if the circuit board material is that opaque black stuff. Also don't get drill cuttings in the hole.
Once you have your hole, make a small wire brush out of three bristles cut from another brush. Chuck the bristles in a pin vise, twist them together, and trim the end flush. Now put a drop of 91%+ isopropyl alcohol in the hole, dip the wire brush in more alcohol, and then gently scratch around in the hole. Do this with the key up and down.
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Well, I've done it: Dissassemled the keyboard and applied fresh silver ink to the bad contact where the original silver contact had broken off.
Now I have to get the whole thing back together. It seems that this assembly needs a firm pressure in order to work properly, especially for the conact spots between the keyboard PCB and the row lines in the plastic. How can I accomplish this? So far, I have been unsuccessful. The plastic rivets are not long enough to allow for an easy re-fixing. Should I use glue? screws? magic, perhaps ;-)
Thanks again, Victor