HP 42S - intermittent rows nonfunctional


I've been a heavy user of my 42S for over 20 years now. To my dismay, I'm starting to see a chronic problem. Most of the time, I lose a row or column of keys.
I'll lose the 123 row or the 963 column.
The calculator has always been either in the old leather case HP used to sell or in use, so it's clean. Is there a way to fix this without having to crack open the case? I've already sprayed contact cleaner in the case and that had no effect other than to make the calculator greasy for a day or so.
I sure am jonesing for RPN. I'm tired of getting a result of zero.


This is likely a problem with deformed rubber at the keyboard connector contacts. This is usually repairable without removing the keyboard overlay.

See the recent thread:

Also see


Hello Rob,

Take a look at this posting. It will show you the foam rubber keyboard to logic PCA contact failure. This is the rubber that needs replacing.

I have done 5 42S upgrades to 32 K as well as restoring about 10 other pioneer models all suffering the degraded foam problem. I use a foam mouse pad as a donor.

opening a 42S

The method I use is credited to Tony Duell and I find the easiest way to enter the calculator. Others prefer to use a credit card inserted between the shells and used to pry the shells apart.

Good luck, and it is an easy fix in the scheme of things.

Cheers, Geoff

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