Dead HP31E


I have an HP31E calculator which appears to have died (... or possibly to have been murdered by me!). When powered up the calculator displays all 8s with the '-' sign showing very brightly. After a while the calculator gradually displays all 9s. Can any one diagnose the problem?

Peter Martin.


Are you using a good battery pack ?
If the pack is dead or missing, and you are using the AC adapter, you may damage the calculator, and you will get erratic operation.


The reason I said that I may have murdered the calculator is because I made the battery pack out of 2 NiCad AA batteries and think that I may have inserted it backwards once. The calculator did work perfectly well with this pack and the fix I did to the contacts. I suspect I may have fried a chip with either dodgy contacts to the battery pack and hence a direct connection to the power supply or the incorrect insertion of the power pack. I've charged the batteries several times and swapped the AA cells but to no avail. The calculator abruply stopped working after a house move. Whether this is significant I don't know; but vibration may have played a part.


Might be the cause, if this is a non-soldered version. Have you tried to squeze the calculator on the sides, and see if behavior changes ?

If you take a look at the pages about the 31E technology, you´ll see the reason for the suggestion.



I've dismantled the calculator and even though its serial number is 1830A17943, indicating a 1978 build date, it is a soldered version.


re: the -8,888,888,888 changing to -9,999,999,999 problem. every time this happens; add 1,111,111,111.

Seriously; running on any kind of battery other than the hp battery pack IS a very good idea, as long as you don't reverse the polarity. In addition to what Renato said about the charger; if the batteries are not making good contact when you are using the charger then you can fry the calc. That means to never let them go completely dead, so you know that you have a good battery connection before you plug in the charger.

It's sad that hp made such a bad recharging system. As a collector i want to have a charger for each calc but as a calculator user i don't want to plug the charger in.


This would make sense. After the move, by the time I got to the calculator the NiCad batteries would have self discharged. I would probably have charged them in the calculator.


Reverse polarity (at least for brief periods) does not seem to hurt these machines. I have seen numerous cases of this without damage. Done it a few times myself... beer helps.

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