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HP Forum Archive 14

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HP 41-CX problem
Message #1 Posted by sreen9 on 23 June 2004, 10:22 p.m.

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...

Thanks, Sreen

Re: HP 41-CX problem
Message #2 Posted by Vieira, Luiz C. (Brazil) on 24 June 2004, 1:28 a.m.,
in response to message #1 by sreen9

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)

Re: HP 41-CX problem
Message #3 Posted by Ronald on 24 June 2004, 4:25 a.m.,
in response to message #2 by Vieira, Luiz C. (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 batterķes or it will not start up nicely.



Re: HP 41-CX problem
Message #4 Posted by David Smith on 24 June 2004, 1:11 p.m.,
in response to message #1 by sreen9

Your ON switch contact may be dirty and need cleaning.

Re: HP 41-CX problem
Message #5 Posted by sreen9 on 24 June 2004, 2:04 p.m.,
in response to message #4 by David Smith

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 ?


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