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HP Forum Archive 20

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HP42s sticking key
Message #1 Posted by William Maidment on 27 Jan 2011, 12:35 p.m.

How can I access the inside of my 42s to try and unstick a key. thanks Bill

Re: HP42s sticking key
Message #2 Posted by geoff quickfall on 27 Jan 2011, 2:12 p.m.,
in response to message #1 by William Maidment

HP 42S

Take a look a the HP SOLVE June issue by clicking the above link. Then scroll down to Calculator Restorations. The second article explains one method of entry into the Pioneers. Not as difficult as it appears.

Cheers, Geoff

Emails on there way to those that have lent me calculators for restorations (with explanations on the delays), bear with me!

Cheers, again, Geoff

An email would be good
Message #3 Posted by db (martinez, ca.) on 31 Jan 2011, 10:53 p.m.,
in response to message #2 by geoff quickfall

You can use the address from one of the emails i have sent you, my home address, or you can use Dave's contact system through the forum.

10 months have passed since i loaned you my hp10 to disassemble and photograph for your book, and since i last got a reply. An email would be nice.

Re: HP42s sticking key
Message #4 Posted by Randy on 27 Jan 2011, 4:56 p.m.,
in response to message #1 by William Maidment

Does the key have the normal travel and click or is it flat with no tactile feedback? If it clicks okay and doesn't register correctly, it is most likely bad contact between the keyboard and logic board.

I find this to be a perfectly acceptable method to open Pioneers:

Personally, I have never seen a faceplate that has been peeled off without some form of distortion or damage. Peeling faceplates to open Pioneers isn't necessary, it puts the keys at risk and is in my opinion, a really bad idea. I've opened *many* Pioneers using the Brogger method and find it the best solution by far.

Re: HP42s sticking key
Message #5 Posted by Diego Diaz on 2 Feb 2011, 12:16 p.m.,
in response to message #4 by Randy


Just to make sure: Sticky key? or Non-responsive key?

The first symptom is more likely related to the key contacts themselves than to the Keyboard/PCB connection.

Some of the carbon-made contacts turns into dust, creating a weak "contact" between the two conductive foils of the keyboard layers, this weak contact is recognized by the CPU as a permanently pressed key.

Regrettably the only way to fix it is by removing the dozens of plastic rivets which hold the steel frame in place (this is the easy part), then taking the key layers apart, cleaning them and (the *very* difficult part) re-assembly the whole thing keeping a high grade of tightness between the steel frame and the top half.

Sorry for the bad news... I sincerely hope you *only* have a non-responsive key, which in most cases just need the replacement of the sponge beneath the KB contact strip; far more simpler as described by Geoff's article.


PS: I agree: removing the faceplate is not required in most cases.

Edited: 2 Feb 2011, 12:22 p.m.

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