HP-21 repair

[rprosperi]

(10-15-2021 07:17 PM)Benoit Maag Wrote:  I have a HP-21 that turns on but only displays a zero on the right of the display, an occasionally 3 zeros across the display. The keyboard is unresponsive. Is that a clear sign the ACT chip is dead or could the problem be caused by something else, such as cross talk between PCB traces, or a defective discrete?

I am not a PANAMATIK, but I'd say it's 95%+ an ACT issue.