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Another HP-21 repair
11-19-2019, 10:01 PM
Post: #1
Another HP-21 repair
I just got another HP-21 to play with (previous one here

This one was presumed dead but could revive it just by installing new batteries. Oddly enough it does not work when connected to the charger (with batteries installed) but it operates normally on just the batteries so all is well.

Some of the keys do not register at all when pressed so I opened it and will clean it tomorrow. If I understand correctly I should clean the contacts with vinegar, then rinse with water and clean again with isopropyl alcohol.

Here is a picture of the unit disassembled


11C 12C 15C 17BII 18C 19BII 21 25 27S 28S 32E 32S 32SII 33C 33S 34S 35S 38C 39gs 39GII 40gs 41C 41CV 41CX 42S 45 48G+ 48GII 49G 49G+ 50 67 71B 97
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Another HP-21 repair - Moggul - 11-19-2019 10:01 PM
RE: Another HP-21 repair - Moggul - 11-21-2019, 09:01 PM

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