Dead HP-31E, where do I start?


I have a HP-31E that is dead and I am not sure where to start.
It is in the box with original case, manuals, and AC adapter.
Serial number is 1920A92944, Made in USA. It does not turn on when plugged in, and when I checked the battery pack I noticed that one contact is broken. The extra piece was under the batteries.
Where do I start with this?
I know this was a lower end model, but I would like to be careful and want to avoid any further damage.


first, do not plug it into that charger. never. if it is dead; that is probably what killed it.

second, you might clean the contacts with vinegar and rinse with alcohol or distilled water if they have blue stuff on them. then note from the battery (it will only go in one way) which is the + and which is the - contact and mark them both as a reference. you probably have some AA rechargables (they are the correct 1.25v). turn the switch to the off position. with some aluminum foil to temporarily make up for the broken contact and to bridge the batteries, you might find that when you switch it on, or after wiggling the batteries, you have a calculator.
if not, and if there was blue corrosion, then you might have to take it apart to clean off or paint on new traces. popping off the back is difficult the first time if you only have three hands but there is a very good set of instructions with photos in the articles section of this site.

there are lots of other things to try, but the're down the list.

Edited: 17 Jan 2011, 5:19 p.m.


Thank you, that did the trick and I now have a calculator that comes on and seems to work in general, but it has a new problem.
The lowest row on the display doesn't come on. Is there any way it can be fixed?


I second that request :-)

I have a 31E with some missing segments. The lower left segments are out for all digits on my 31E.


it might be the pressed-on chip problem. maybe.

if you post the serial numbers, someone here will know if yours are from before hp started soldering stuff onto the pcb, without having to pop it apart. like i said; taking the back off is not difficult. however; each time you spring it open you run the chance of cracking something. but putting them together is like falling off a log.


Thanks db. My S/N is 1849A24700 Made in USA


We had this topic recently: IIRC, you can't differentiate soldered/solderless by s/n but you can easily by weight. Please search the forum. HTH


I don't have a battery door and I'm at 171g weight. I think this means solderless and not good for me :-(


Click here


That looks good. I also found a link with some pictures and a different method for separating the case. Not sure who made this page, but it may be helpful.


I've used that method. It works fine too. I just wished i had longer fingernails and more fingers. I don't know who made that page either. Nicely done though.


You lucky man - I swapped my HP31E for an HP32E (and quite a lot of cash) way back in 198x. Don't regret it but the HP31E is now definatly a collector's item...

Mike T.


i have two 31E's here, which i had planned to 'retro fit' with larger modern LED displays. should i be holding off on this plan?

both seem to have small bubbles in the plastic lenses over the LEDs, along with some frosting. and both are well-worn, though at least one functions ok.

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