HP-25 problem


I have an HP-25 whose display runs unstoppably when the calc is switched on. (I'm running it from the charger because the battery pack is shot, and I have no other.) Pressing any of the buttons makes no difference, nor does switching the w/prgm switch.

As far as I can tell, the display is cycling through all the digits wildly, much as it might while a program is running. (Except for no blank-outs.)

It acts like it's channelling the universe of numbers in a kind of psychotic fugue...

I'm fond of the little guy, and I wonder if there's anything that can be done. This is not an urgent crisis, since I have other HPs (35, 67, 32sII) to keep me in crunched digits. However, it would be nice if the whole famn damily were in running order.

Any suggestions?

Thanks in advance --

Robert Burnham


Funny you should mention that. I have a similar issue with my 25, but only when its on the charger. When I turn it on with just the battery, it works fine. I wonder if the infamous "ACT" chip is just "ACT"ing up...



First off, you need a GOOD battery installed in the machine... without one you get the display that you talk about and often times a burned out machine.

Second, you may have corrosion or contamination on the circuit board... usually green on and/or under the bottom chips.

Finally a blown ACT chip... the 22 pin big one near the bottom of the circuit board.


My HP-25 does the same as yours if the battery is not connected properly, or if there is an old bad battery fitted. The power adapter relies on the battery to smooth the voltage. BEWARE... it may cause damage if there is not a good battery fitted.


Thanks for the advice. It does have slightly corroded contacts on the two prongs that touch the batteries, so I'll clean them as best I can. (I'm thinking Q-tips moistened with Windex.)

Then I'll take the battery pack apart and install new ones, perhaps going the route of a custom rebuild at Batteries Plus.

If all this fails, the little guy will be a goner because I'm not up to trying brain surgery on any chips or trying to swap old ones out. It'll become a display item.

So -- thanks again for your help! Much appreciated.

Robert Burnha


Try the NiCad Lady http://www.nicdlady.com/ or TNR Technical http://www.tnrtechnical.com/. They both have extensive experience rebuilding HP battery packs.



It is easy to rebuild the battery pack yourself.

Just neatly cut through the plastic bar near the contact end of the batteries and lift them out after making a note of the polarity ( I made a red dot on the plastic holder at the + side with a permanent marker). Clean the spring and fit new NiCad or NiMH battries, carefully sliding them in under the plastic bar, dont bend it up more than is necessary. Then refit to the calc.

Good luck!


Also gently sand the contacts with fine grit sandpaper. Another useful trick is to put a small wad of aluminum foil on top of each battery contact.

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