The Museum of HP Calculators

HP Forum Archive 01

[ Return to Index | Top of Index ]

Flakey HP41CX clock?
Message #1 Posted by Chris Morris on 24 Nov 1999, 4:02 p.m.

Anyone else had this problem? I have two HP41CX's, one is a halfnut. Both seem to suffer from a lack of robustness in the clock department. On powering up, I sometimes find the clock has reset itself to 00.00.00 etc. Yet the stack registers are all preserved ok. Are the clock registers less robust in the face of minor battery interruptions or is there another factor at work? Similarly, if the battery is down - "BAT", the clock by design won't come on - fair enough. But if one inadvertently asks for the clock display, surely this should not lead to a clock reset. How long can the clock keep time 'batteries out'. The regular memories go on for days in this condition.

      
Re: Flakey HP41CX clock?
Message #2 Posted by Pete on 25 Nov 1999, 9:05 a.m.,
in response to message #1 by Chris Morris

>>>Anyone else had this problem? I have two HP41CX's, one is a halfnut. Both seem to suffer from a lack of robustness in the clock department. On powering up, I sometimes find the clock has reset itself to 00.00.00 etc. Yet the stack registers are all preserved ok. Are the clock registers less robust in the face of minor battery interruptions or is there another factor at work? >> Similarly, if the battery is down - "BAT", the clock by design won't come on - fair enough. >> But if one inadvertently asks for the clock display, surely this should not lead to a clock reset. How long can the clock keep time 'batteries out'. The regular memories go on for days in this condition. <<

Boy, I'm sorry. It's been quite a while since I played with one of these to any great extent. Another possibility is get your manual out and double check all the user flags status. Also, much less likel;y, there may be some quirk in a program causing this condition even if it is totally unrelated to any time function. Good luck and let me know if anything happens.

            
Re: Flakey HP41CX clock?
Message #3 Posted by Steve on 25 Nov 1999, 7:17 p.m.,
in response to message #2 by Pete

I just subjected my 41CX to a 10 second power disruption (similar to changing batteries I guess) and the clock continued to run. (well, I didn't lose the time)

How long did it take to lose the time?

                  
Re: Flakey HP41CX clock?
Message #4 Posted by Chris Morris on 26 Nov 1999, 12:32 p.m.,
in response to message #3 by Steve

Thanks Steve. For the '85 CX halfnut with regular N cells, time sometimes has been disrupted without even removing batteries, clock will read e.g. 3 am, implying it got reset on its own 3 hrs ago. For the '83 CX with the rechargeable pack (83120A) when the low battery icon comes on, if I inadvertently request clock time the display blanks (by design?) to not show clock when the battery is low, HOWEVER after recharging the clock has reset itself. Maybe I'm just unlucky enough to have two different problems, but I notice the stack registers are always retained in both cases when this this happens - so why does the clock register fail first? It doesn't seem to relate directly to a 10 second or longer battery disconnect.

                        
Re: Flakey HP41CX clock?
Message #5 Posted by Steve on 30 Nov 1999, 7:39 p.m.,
in response to message #4 by Chris Morris

Last night I went looking for my CX manuals in order to try to find out how long the clock would work without batteries (and other conditions). Unfortunatly the manuals have gone into hiding :-(

Your problem does sound a bit like a fault to me. Perhaps the capacitor in the CX that holds power during battery replacement is dead or dieing and it is causing the problem?

But to two CX's that you happen to own??? And as to why the rest of the calculator doesn't die....?

Do you have any corrosion on the battery contacts?

Has the calculator been repaired or modified?

I don't think I can offer even a slightly educated guess. It's weired. Keep us informed if you do find the cause.


[ Return to Index | Top of Index ]

Go back to the main exhibit hall