|Re: HP 29C 1-2-3 keys not working|
Message #12 Posted by Randy on 3 May 2007, 3:41 p.m.,
in response to message #11 by Eric Smith
Olivier, back in January, I sent you a photo so that we could identify which version of keyboard you had. I never heard back from you about this until a few days ago at which point I had forgotten about the earlier exchanges.
For the sake of those trying to help and to avoid duplication of effort, lets pick up that thread here publicly.
I've posted that photo originally sent below. I've added a small white circle and line pointing to the area that I think is the problem. I said I think it is the problem because I'm making an assumption about which version keyboard you have.
If memory serves me correctly, all 29C keyboards I've seen use snap domes formed on a plastic sheet, similar to the later 30 series keyboards. This is very different from the formed strips of the classic keyboards which were used on the early Woodstocks. The photo shows a 25 keyboard on the left with the flex strips, the keyboard on the right is a later model 29C keyboard with plastic domes. Notice that on the 25 keyboard you can see metal through the holes where the contacts are. There are no holes on the 29C keyboard due to the differences in construction.
The problem is most likely caused by a failure of the plastic heat stake(s) that hold the epoxy fiberglass part of the board against the flexing domed sheet. The heat stakes fail and the two halves loose connection(s). The area that I have circled is where the connection is made to the common of your keyboards problem row. The plate-thru hole connects to the tear-drop trace you can see through the board. The large circle is where the common of the plastic dome sheet connects to the circuit. It is only the pressure created by the surrounding heat stakes that hold them in contact. If the heat stakes fail, as is typical in that area since that is where most of the battery corrosion occurs, you're left with an intermittent keyboard.
Given the design of the molded part that has failed, there is little chance of a permanent repair. Any use of epoxies or the like will only result in frozen, non-moving keys. Small screws cannot be used as the surrounding plastic is only the diameter of the heat stake that has sheared off.
If that is indeed what has happened to your keyboard, I'm fresh out of ideas that would fix it.
Edited: 3 May 2007, 4:50 p.m.