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HP Forum Archive 19

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HP 41CX Auto power-off problem
Message #1 Posted by Jose Poyan on 17 Apr 2009, 4:31 p.m.

Hi all, I just bought a faulty HP 41CX. I fixed it; it was just the usual cracked back. Now it turns off after only 20 seconds all the time. This can't be normal! It didnt come with manuals so I'm searching for some help in the Forum(I didnt find this problem already posted). I'm using a fully charged battery pack. No "BATT" message is shown in the screen; it just turns off.


Oh I forgot: although I didnt fix the back of my calculator tight enought, I can leave the screen in watch mode and I stays like that; so its not a contact problem.

Edited: 17 Apr 2009, 5:49 p.m.

Re: HP 41CX Auto power-off problem
Message #2 Posted by Dan Grelinger on 17 Apr 2009, 9:10 p.m.,
in response to message #1 by Jose Poyan


I can't help very much, but here is what I know, or suspect:

There is no normal function that would change the HP-41's auto-off functionality as you describe. Therefore, the manual will be of no use to you with this problem.

When the clock is in the display, the calculator is actually running a routine every second to update the display. I assume that if you use the calculator, or have a user program running, it won't turn off. This would indicate that it is the auto-off functionality that is turning the HP-41 off, just not after the 10 or so minutes it is supposed to wait.

I believe, from some long ago reading, that the auto-off functionality is located in the display controller. Not knowing much about the internals, I would not be able to rule out a contact problem (there are plenty in an HP-41), but it may be a faulty display controller.


Re: HP 41CX Auto power-off problem
Message #3 Posted by Andrés C. Rodríguez (Argentina) on 18 Apr 2009, 9:48 a.m.,
in response to message #2 by Dan Grelinger

I'm not familiar with the CX specific features such as clock or timers, but I suggest you can explore the ON function (XEQ "ON"), which prevents the calculator from turning off after 10 minutes.

The 41C and CV CPU have 3 states: Runnning (when actually performing calculations), Idle (just displaying data) and Sleep (no display, just status and memory contents are preserved).

Re: HP 41CX Auto power-off problem
Message #4 Posted by Monte Dalrymple on 17 Apr 2009, 11:30 p.m.,
in response to message #1 by Jose Poyan

While the clock is displayed the cpu is running. When the cpu goes idle there is a time-out function that powers down the cpu after 10 minutes. This timer is actually in the display controller, BUT the capacitor that determins the time constant is on the cpu board. If this specific connection is bad, or the capacitor is bad, the time-out time will be much shorter than the default 10 minutes. This is probably the cause of the symptom you are seeing.


Re: HP 41CX Auto power-off problem
Message #5 Posted by Garth Wilson on 18 Apr 2009, 12:20 a.m.,
in response to message #1 by Jose Poyan

To get around it until you get it fixed, you should be able to use the ON function to make it ignore the timeout, right? That's part of the startup routine on mine all the time. I always turn it off with a program assigned to a key, which sets flag 11 (the autorun flag) before executing OFF. then when I turn it on, it checks to see if there's anything in the DAYTIMR file it's supposed to remind me of that day, and if not, sees if there are any alarms set and show how much time is left, otherwise move on to show the time and date. (Yeah, it takes a couple of seconds.) One of the other things it does is to set the continuous-on flag, flag 44, with TOGF in the ZENROM. I'll be the one to decide when it's time for it to go off! The calc is 23 years old and has never shown any signs of a bad connection except that it forgets what the time and date are if I drop it, but I suppose the auto-turn-off time could go wacky and I wouldn't know it. I don't think that has happened yet though, because if an alarm turns it on and it doesn't go through the same start-up routine, it will indeed stay on for something like ten minutes by itself if it's not a control alarm with a program that turns it off again.

Edited: 18 Apr 2009, 12:23 a.m.

Re: HP 41CX Auto power-off problem
Message #6 Posted by Jose Poyan on 18 Apr 2009, 3:29 a.m.,
in response to message #1 by Jose Poyan

Fixed it ! I opened my 41cx once again yesterday. Even when the contacts look shiny, they where not making contact. This morning it keeps running and doesnt turn off. Thanks all of you for the help.


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