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Hello everyone, I recently acquired a "mint"
condition 41-CX, but it has the following problem:

It does not turn on by pressing ON key or
even ON and backspace keys together. I have to
remove the batteries for a couple of minuites
and re-install them, and then do a ON+backspace
or a ON+ENTER a few times to turn it on.

I have heard that some 41s have this kind of
a problem. is there a fix for this other than
removing and re-installing the batteries ?

I appreciate your help with this...


Hello, Screen9 (whoever you are...8^)

Have you checked for the construction type? This "freezing" behavior is mostly common to the halfnuts.

If the batteries contacts are faulty (not permanently), I mean, if because of any reason the batteries fail to maintain power to the nut IC for sometime or if the voltage drops to some value not enough to power it up, it may lock. Under normal voltage supply, it is not something that happens so often.

If it returned to normal operation, I'd just observe it for some days. If it happens again, a good cleaning procedure in the batteries contacts is sometimes enough. If not, opening the calculator and cleaning the internal connections in the same battery/IO assembly with the mainboard usualy solves the problem.

I'm delving into a faulty HP41CX (that belongs to a very good e-friend of mine) for some time and I'm also in the need for some diode characteristics. Have anyone read this post and willing to help, I'd like to know the specs (or replacements) of the diodes found in the HP41CX fullnut mainboard (if I am not wrong, there are four or five diodes). Thanks in advance.


Luiz (Brazil)

I did a measurement of the startup power the half nut needs:
over 400 milliampere, dropping in a second or less to 1 - 2 milli amperes as normal run-rate consumption. This means you need to have decent batteríes or it will not start up nicely.



Your ON switch contact may be dirty and need cleaning.

It is OK now !

I entered a small program, and the 41cx
got stuck with the message "packing".
I removed and re-inserted the batteries,
and did a "backspace+ON" and got a "memory lost".
Now, I can turn it ON and OFF with the switch.

I noticed the following:

1. The 41CX never gave the "memory lost" message
when it turned ON by doing "backspace+ON", just
displayed the previous screen.
2. When I entered the very first program, I noticed
a lot of "junk" instructions in the program
memory (by doing SST).

Thanks to all for trying to help.
(BTW, it is a halfnut)

David, how do I clean the switches on the 41-CX ?
Can you tell me or point to a procedure ?