I've bought an old HP 67 calculator (SN 1702) some weeks ago.
After fixing the battery charger (thanks to Tony Duell to make me look at the fuse), I would like to make the keyboard work better : some keys have a bad feeling (0...9, +, .), some keys register multiple copies of the typed character(2,5), some keys don't even work(C,D,E).
After opening the case (without peeling the label : just with a little cross shaped cut along 2 diameters upon both holes, then carefully lifting the 4 angles of each cut, unscrewing ... and the same in reverse order to close back. The label looks about as before, but I'm not a purist... ;-) ) it appears that the metal strip is broken under the 12 key : 10 numerics, "." and "+". The broken "2" spring is almost flat.
To fix the C,D,E problem (key springs mechanically like never used) I follow the way described by Steve Loboyko ("Bad keys and What to do About Them") only replacing the sandpaper by a paper strip soaked in alcohol : it works.
First question :
- is there a quicker way, with a voltmeter, to test the result of cleaning without having to close the calc and using normally the keyboard : for instance putting the first continuity probe on the ENTER metal strip, the second one on the golden hole immediately beneath the strip, and then pressing the key, we get sound. The same method can be applied to some couples of (key / hole), but I couldn't find the complete mapping : which hole (or which electric trail) for which spring ? Is there any plan available ?
Second question :
- is there any way to fix broken springs (for instance by putting a new spring under the broken one) ?
- can I avoid the double or triple typing with the "2" key ?
Thanks in advance for any help.