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HP Forum Archive 18

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29c "Error" on power up, then works fine
Message #1 Posted by pespen on 25 July 2008, 1:17 a.m.

Hi, I have a 29c with rebuilt NiCd battery pack in place and the 29c is attached to a charger.

Even if battery is in place and charger attached, the 29c will usually power up and display "Error". A Clx and then the calculator works fine. If I turn the 29c off and then back on again in less than a minute or so, it retains values that had been stored before the power off, even under just battery power. However, if I turn the 29c off and let it sit powered down but with battery still in place and charger still attached, it displays "Error" again and the continuous memory contents are gone.

Otherwise, the 29c works fine.

Any experts know what might have failed on the 29c

      
Sounds like
Message #2 Posted by Geoff Quickfall on 25 July 2008, 2:24 a.m.,
in response to message #1 by pespen

and I probably have the terminolgy wrong, the super capacitor. The capacitor is losing it's charge to quickly or the trickle charge to the capacitor while the batteries are in place and the calculator is off is now defunct.

Tested mine and it will sit for weeks with the internal programming in place. I get about 20 hours with the batteries out and of course not hitting a switch, from the capacitor alone.

Identify the capacitor and replace with a similar type, I am sure some here has a wiring diagram or suggestion.

Cheers, Geoff

PS at least it isn't the memory or IC chip that is US.

            
Re: which is the magic 29c capacitor?
Message #3 Posted by pespen on 25 July 2008, 2:56 p.m.,
in response to message #2 by Geoff Quickfall

I suspect a leaky capacitor also. I'm up for finding a replacement capacitor and replacing, but I'm not sure which one it is.

The following shows the internal of the 29c:

http://www.hpmuseum.org/29cint.jpg

If some knowledgeable person could tell me which of those capacitors is the one that "powers" the C-MOS memory when the calculator's off?

Quote:
and I probably have the terminolgy wrong, the super capacitor. The capacitor is losing it's charge to quickly or the trickle charge to the capacitor while the batteries are in place and the calculator is off is now defunct.

Tested mine and it will sit for weeks with the internal programming in place. I get about 20 hours with the batteries out and of course not hitting a switch, from the capacitor alone.

Identify the capacitor and replace with a similar type, I am sure some here has a wiring diagram or suggestion.

Cheers, Geoff

PS at least it isn't the memory or IC chip that is US.


      
Re: 29c "Error" on power up, then works fine
Message #4 Posted by Bram on 25 July 2008, 5:49 a.m.,
in response to message #1 by pespen

The error message when switching on is a documented indication that the power has been lost and so have the memory contents.
I myself donít connect the power supply to any Woodstock ever anymore; Iím too afraid of frying the precious device. Moreover, thereís no need to. Already a long time ago I removed the middle bar from the batterypack, which allows for easy replacement of the batteries with recharged ones or even disposable AA batteries. This way nothing can go wrong.


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