HP-45 keypad problem


I have an HP-45 which is displaying the following symptoms:

The keys on the lowest row are not doing their proper function. In particular:

[divide] acts like +

0 acts like ENTER, and [Last X] acts like DEG

. acts like CHS, and [pi] acts like RAD

[sigma+] acts like EEX, and [sigma-] acts like GRD

I suspect that a signal line is bad, but I don't know how I would go about repairing it. Any suggestions?


Most likely is some corrosion or (often invisible) grunge on the keyboard or CPU board. Open the machine (remember there are two screws under the upper corners of the rear label and under the two bottom feet) and clean everything with 91%+ isopropyl alcohol.


Hi Mark,

David is right, you can safely use Isopropanol to clean the electronics or keyboard contacts, but if you have it at hand, you may be tempted to use it to clean other parts (such as the plastic shell or keyboard legends) with it, too - DON'T DO IT !
It's a typical mistake of newcomers to HP restoring. Be warned.
These plastics may turn white and the keyboard legends will
disappear under the white mess.


I have found that Armor All will clean up the white residue on the case.

For cleaning the plastic cases of grunge, label residue, and marker ink, I have found that white gas (Coleman camping fuel) works very well. It does not affect the display lens, but keep it off the keyboard area. Also best to test your solvent on some very inconspicuous place first.

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