HP12c Platinum Keyboard repair

[Martin Hepperle]

Hello,

attached is a brief description of how I repaired a broken key on an HP 12c Platinum calculator. Yes, a few more pictures would have been fine, but the calculator is already closed again.

While I am quite happy for the moment with the result there may be better methods - feel free to comment.

Martin

[striegel]

(09-08-2015 01:22 PM)Martin Hepperle Wrote:  ... brief description of how I repaired a broken key on an HP 12c Platinum ...

This looks like a great approach. I'm curious about a few details:

• What contributed the helical spring, a ballpoint pen?
• Is the glue expensive?
• Has this changed the feel of that repaired key?
  

I much prefer your mechanically fastened approach using a real spring material to just re-gluing the broken stump.

The HP palmtops (95LX, 100LX, and 200LX) have always suffered the same key fatigue and I've never been happy with the results of using cyanoacrylate (Super Glue).

[Martin Hepperle]

(09-08-2015 05:19 PM)striegel Wrote:  ...

• What contributed the helical spring, a ballpoint pen?
• Is the glue expensive?
• Has this changed the feel of that repaired key?
  

...

• The spring came from one of my "you never know when it may be useful" boxes. It may originally have come from a dismanteled keyboard. The spring inside a ballpoint pen is way to thick. I think you can also buy straight pieces of thin piano wire in a well sorted hobby shop (e.g. for railroad and model aircraft or ships). Not sure whether they go down to 0.25 mm. Another source may be a watchmaker (if this profession still exists), your children's toys, ...
• The glue I mentioned is available in Germany. I am sure that similar brands exist in other countries. It is a 2-component glue, one component is yellow/brownish, the other component is a white powder. It is about the same price as Epoxy glue, but seems to be better suited for plastic material. Epoxy will probably not work very well as it does not adhere well to ABS. There might be even better industrial glues for ABS.
• the feel is the same - I might just have been lucky with my spring selection. Anyway, the most important "click" feel comes from the steel membrane switches on the PCB. Of course this steel membrane part must still be in good shape.
  

Martin