HP-67 keyboard restoration

[Pierre Brial]

Hello,
A friend of mine, retired university teacher, make me a great gift : an HP-67 in very nice condition, with manual, pouch, some cards ... !
The calc in in working order, but the keyboard is unreliable : keys sometimes don't register despite the 'click', and sometimes they register twice. A bit disappointing given hp keyboards reputation (I have got an older HP-35 which doesn't have such flaw).

Did you already experienced this problem ? The procedure described in http://www.hpmuseum.org/howtohp/howtohp.htm recommend the use of sandpaper to clean the gold plating. But may be there is a softer way to do ?

[Jose Poyan]

Hi,
I have exactly the same problem with the "0" key on my hp-67, samtimes it doesnt work, sometimes it marks twice. Besides the keys seem to be lower than they should, they are loose and rattle a lot, do you have this problem too? I wonder if it has something to do with the loose of contact. I didnt open mine yet, but it'll be interested to see what you find.

regards,
jose

[Pierre Brial]

Hi Jose,

I don't have this rattling problem on the HP-67, but I did have it on an HP-45. There are metal strips under the plastic keys, which give to hp calcs keyboards their distinctive click. Theses strips were cracked, and even cut on some keys. So keys losed their firmness, and the electrical connection was lost on cutted ones. Il repaired the connections by soldering tin on the cracks, but I lose the elasticity of the keys.

Regards

Pierre

[Jose Poyan]

I see...
Which strips were broken on your hp45? The bent strips or the contact strips on the pcb?

As I said I dind't open my hp67, but I can tell you about a repair I did on my HP34c last week.

I bought from ebay silver contact paint that comes in small 3 grams glass tubes, for £4. I used this paint to cover the metalic strips on the pcb. I used it too to paint the contact strip on the membrane that was broken for the key "1" (my version of hp34c uses a plastic membrane for the keyboard, with bubbles on the keys and metalic strips for contacts)
This failed becouse the bubbles deform when pressed and the paint is not elastic.

Then I bought cupper tape, that are used in plants to avoid insect, and you can get from ebay for £3, and it's the same as the aluminium tape but cupper one.
I cut a very small square. The glued side is not conductive, so I turned it over almost from the middle to make a doble conductive tape and I left a thin strip with glue. I put it under the membrane, and it worked. Most notable I didnt loose the elasticity of key "1", it feels exactly the same.
Yes, I scratched a little with my screw driver on the pcb, but it didnt mind since I completed the scuffs with Silver paint which proved to be very conductive.

I suggest you to use Silver paint for the contacts. Please let me know if you find the bent strips bronken when you open your hp67.

regards,
jose

[Pierre Brial]

Yes it was the bent strip that were broken. Good idea the cupper tapes.