HP 35s missing keystrokes

[jebem]

My 35S s/n CNA72800051 still works fine, but I use it just occasionally. However, it sometimes do not power ON at first try, but I do not see this as a real problem. Usually I just replace the batteries with fresh new ones and the issue goes away.

I think the "C/ON/OFF" key is a special function one, so the issue can be related to other causes other than a key mechanical failure.

Is the key issue happening on any operation, or is it happening to specific operations, like when cancelling a function or stopping a long running program, or Powering ON or OFF?
Other members have reported that when the "busy" annunciation is on, keys are missed as well.

I would make sure the batteries are fresh, as some issues can be triggered by poor quality batteries. If you have access to a multimeter, remove the cells, and make sure the reading values are identical on both cells and above 3 Volt.

Also, the self-test can help to check the keyboard (C+XEQ).
The calculator may lose the memory contents when running the self-test.
http://www.rskey.org/~mwsebastian/selfte....htm#hp35s