HP 29C keyboard repair?



#9

Hi all,

once more I'm trying to repair a woodstock keyboard, this time in a HP 29C. One of the keys is not working, and I have no idea how to fix this. It looks like there are two different types of keyboards in the woodstocks, one 'old style' that has a small hole under every key contact, and a newer one that doesn't. This is one of the newer style. It appears that its key contacts are no longer spot welded metal, but plastic domes.

Does anyone have an idea how this could be repaired? Do I have to take it apart and re-apply some sort of conductive material to the contact? And where would I get this in Europe?

Thanks for any help, Victor


#10

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.

#11

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


#12

The dome looks intact. Where would I get this conductive ink? I live in Switzerland...

Thanks, Victor


#13

Hi Victor,

any electronics shop should carry it. It's sometimes called 'Leitsilber' in german. Apply it with the finest brush you can find (or cut away some bristles of a not-so-fine brush). Don't forget to shake the bottle very well.

Thomas


#14

Thanks, Thomas. Read it, went there, bought it - I'll do the repair work tomorrow, and I'll keep you posted.

Thanks everybody for the great help in this forum. I love it!

Cheers, Victor

#15

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.

#16

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


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