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Another HP-21 repair
11-21-2019, 09:01 PM
Post: #3
RE: Another HP-21 repair
(11-20-2019 10:24 AM)Maximilian Hohmann Wrote:  If it is entire rows or columns of keys that are not working then the cause is usually one of the contacts which connect the two PCBs. Single bad keys are caused by the key contact or by corroded traces on the keyboard PCB. The easiest way to troubleshoot keyboard and display problems is to interchange these parts between different calculators. This can be done safely.

Thank you Max for the help!

I cleaned the keyboard PCB which had a lot of green oxide and reassembled the keyboard but the same keys still didn't work. Then I swapped the keyboard with another (non working) unit and the problem persisted so it must be the contacts. I will try again this weekend and clean everything.

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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