HP25 keypad problems

[Dave Britten]

(06-23-2020 03:25 PM)calc-calcs Wrote:  I have a HP25 that had the typical internal corrosion problems, but was easy to clean up internally at the usual spots and is now fully operational. Only remaining problem is with some of the keys, specially the 2 and 5, even tough they still have the right feel, but seem to have a lot of bounce and when pressed once usually cause multiple entries, or none at all. This behavior goes away after giving the key a bit of a workout and in general after that they start behaving normally again. But if left unused for more than a day or two the bouncy behavior returns. My guess is that there might still be some active corrosion inside the contacts and/or dirt getting in the way.

I know its not an easy task to disassemble the keyboard in this series, and even less to put it back together. So far I tried to get a drop or two of IPA 91% between the key and the front, but it only seemed to help marginally if anything at all. My guess there is a build-in splash barrier preventing the alcohol to even get close to the actual contacts.

Has anybody fixed a keypad problem like this one in any hp2x without necessarily having to disassemble it for the contact cleaning? I'd be willing to try anything reasonable before embarking on taking it apart, although guess the process might have a favorable outcome as long as I can be put back together afterwards and still remain reliable.

Thank for any ideas.

You shouldn't have to do anything extreme like fully disassembling the keyboard, but you'll need to open up the calculator and remove the circuit board, which is very easy to do on Woodstocks (there are plenty of pictures and instructions floating around if you need them).

Get some Deoxit D100L:

https://www.amazon.com/CAIG-LABORATORIES...B0000YH6F8

Put a very small drop of this into the tiny hole in the PCB behind the affected keys and work it in by exercising the key. I've used this technique to fix bouncy/hesitant keys on my 25 and a couple 41s, and it works great. Note that the key may feel and sound a bit different for the first day or two, until the Deoxit dries.