HP-41CX beeps when turned on !!


I recently acquired an HP-41CX that looks in great shape; however, when inserted new batts and turned on, it just beeps (continuously), and doesn't respond to any key (incl ON key).

Any ideas ?


Try to remove batteries, press and keep down "<-", tap "ON", then release "<-" procedure. Put batteries back and try to start it again.

If you still have a problem, try to get a diagnostic module and see if it can take control and tell you what is wrong.

Does it emit a high pitched noise or is it just a continuous beep?



can you tell us if it is a coconut (fullnut) or a halfnut? Coconuts have the well known problems related to broken posts, and chances are that yours is suffering from this kind of trouble. To identify one for another:

Let us know about your findings, please.

And success!

Luiz (Brazil)


Followed Hakan's procedure and it stopped beeping (it was a high pitch beep). It doesn't turn on though.

It is the half-nut model.

What is the next step? and thanks !


Hi, Giovanni;

you may want to repeat Hakan´s procedure a couple of times again (as many as you need) and see if the calculator gets back to normal.

There is one straight procedure that is explained in the HP41 manual: leave the calculator without batteries for a couple of days (the C/CV may need about four to five days) in order to discharge all remaining electrical charges in all capacitors (it is known that the HP41 has two 'big' electrolytic capacitors). Because it uses low-power C-MOS technology IC´s as load, these capacitors take too long to get rid of remaining charge. The HP41C/CV (not the CX) may retain RAM contents for hours without batteries. The CX has the internal clock and extra RAM circuitry so discharging is faster.

There is also the electrostatic charge, different of the one found in capacitors due to regular operation. I had once to disassemble a coconut and 'resurrect' it after discharging the capacitors and leaving it over an aluminum foil, carefully pressed in the side without components so all terminals were shorted wit each other. After about an hour it was singing and dancing again.

Hope you succeed.

Edited: 19 Feb 2010, 1:20 p.m.


Hi, Luiz!

You've been gone for awhile from the forum lately. I hope all is well.


Hi, Doc;

main reason: classes have already begun and particularly in the university I teach at, many structural changes took place and, as you know, teachers are always the advanced front in the battle...

Appart of that, no problems. Should I have a 36-hour day, I´d use the extra 12 just for experimentation in my (humble) lab. Even in our 'carnival' week I took it for solving some issues.

Cheers and thanks for asking (in time: you have mail...)

Luiz (Brazil)


Thanks guys. Will let you know in a couple of days.

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