Another HP-21 repair

[Moggul]

(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.