hp 21


the two keys "5" and "6" of my HP21 doesn't work any more. After opening the calculator, I can see on the back side of the keyboard lines and columns of copper holes : everything seems mechanically OK. Is there another way to fix it than breaking :-( the small plastic links and looking inside ?


Yes, this is an all too common problem. It is also easy to remedy. Take around three bristles from a small wire brush and chuck them in a pin vise or razor knife holder. Trim their ends even. Place a drop of 91% isopropyl alcohol in the hole behind the offending key and gently "scritch" around in the hole with the wire brush. Be careful not to break a bristle off in the hole. This also works for HP41 keys.


thanks for your tips : it works fine

"merci beaucoup"

P. Voinot


You can find previous postings here about how to clean contacts with alcohol, compressed air, etc; or brushing with a tiny piece of wire. Read the postings before doing any work.

If possible, avoid breaking the posts. If you need to cut them, try to do it in a manner that allows for subsequent glueing or otherwise sealing them when you are finished.

Many years ago my HP25 was fixed by the then "official" HP service in my country (there were no HP offices here at the time); they cut the top of the posts, and the keyboard became somehow loose, losing some of the original feeling.

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