Opening an HP21


Sorry to bother you again on how to open an HP21, this was probably answered 1.22e44 times already here.
I got it from my hair cutter (seems everybody knows I'm a calculator nut).

The machine has dead batteries, + and - keys stuck, and the display flickers when on the charger alone.
I'd like to clean up the keyboard and test operation with AA batteries.

Any help would be appreciated.
Note that these questions could be answered once and for all in the Articles section...


It is very easy to clean the keys on most Woodstock series machines (and 41C series machines). Take three bristles from a wire brush and chuck them up in a pin vise or Xacto knife holder. Trim their ends even. Behind each key on the back of the keyboard is a hole. Place a drop of 91% alcohol on the hole, dip the ends of the wire brush in more alcohol, and "scritch" around in the hole. Don't break off a bristle in the hole... that can be bad news. I have seen one Woodstock keyboard that did not have the holes under the keys... more bad news.


Be careful not to use the calculator with AC adapter only because the voltage is not regulated.


Thank you for a very helpful set of answers - and sorry for not figuring out the disassembly page myself !
Regards to all.

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