Hello,

Yesterday I got a HP-34C with the "1" key not working. Some time ago I fixed the keyboard of some 32Es. During these repairs some questions and some discoveries occured.

In the following text I will talk of a "foil" and a "board". foil means the plastic-sheet that contains the small raised bubbles which are pressed by the keys above. The board is the plate connected to the foil, but without the chips etc. (At least at the solderless version)

1.) It is possible to swap the keypad (board plus foil) between HP-32E and HP-34C. I think this is possible for all spice-series calculators. Both calculators were solderless versions. Does the keypad exchange also work between a solderless and a soldered calculator? (I didn't open a solderless spice until now. Are the chips soldered to the "board"?)

2.) Keypad connection repair:
Sometimes several keys fail at once. I found out that this happend when one (or more) of the connections between the foil and the board get separated. The connections are 4 or 5 circular spots between the bubbles with a diameter of about 3mm.

It helps to place a small piece of tape over the connections, so that they are pressed together with the calculator closed.

It also helps to press a soldering iron on the connection spot. (This burns through the foil). But if the spot gets to hot, the circuit path comes off the board. AARGGH!

Principially it is possible to completely remove the "foil" from the "board" and resolder it. But only once or mabe twice!

Are there better repair techniques? And is it possible to restore the circuit pathes with a silver-pen or something like that?

3.) "foil"-repair
The HP-34C had another problem with only one key not working. I found out that the small sheet of conductor which is placed inside the key-bubbles was broken. I tried to glue some aluminium foil of the same size in place after removing the "foil" as mentioned above. The aluminium foil didn't get electrical contact with the original conductor strip. So I soldered a very small connection between them. This worked, but flattened the bubble, so that the key-click dissapeared for that key.

The HP-34C repair ended with the former bad key working and several other keys not working due to losened circuit pathes. :-( So I slaughtered an HP-32E and successfully worked with a donator keypad...

Does anyone of you know better techniques for the "foil"-repair?

Please excuse my english and the wrong technical terms; my language abilities aren't the best today. :-)

Holger

12345 to remove

I believe that some early "E" series machines had a different layout to the keyboard. On these machines the battery backup connection to the RAM chip is not present. You might be able to do some cutting and jumpering to provide it though.