25 and/or 25c Repair


I recently acquired a couple of 25's (actually, a 25 and a 25c). Both had what appeared to be replacement batteries and the the battery pack holder modified to accommodate the new batteries. A wall charger was included with these. Neither unit would power on, so I assume the batteries are shot. I did not plug them in for fear of frying them. In the 25, I tried a fully charged, fairly new set of NiMH batteries and still no power.

At this point, I suspect the previous owner may have tried plugging them in via the wall charger and perhaps they are already fried. Does anyone have experience diagnosing these or any suggestions as far as who I could send them to for repair/diagnosis? It would be sweet if these were more than just "display" models (attractive as they may be). :-)


J Grim


I would suggest contacting fixthatcalc

Unfortunately, if those calculators, codenamed Woodstock, are connected to the AC adapter w/o a good NiCad battery pack installed, serious damage usually occurs to the electronic components.


Thank you. I had read that that might be the case. I don't know if the previous owner did plug them in or not, but I am afraid that he did. Oh well, if they are not repairable, at least they are nice to look at and I did not spend that much to get them.

Thanks again,

J Grim


Hi J!

Don't give up yet. You've got nothing to lose by opening them up and seeing if corrosion is the problem. Have you tried connecting an external power supply to the battery contacts?? (Not a supplied charger, but 3V directly?) Usually, when these are powered incorrectly and the ACT chip goes, there should still be some kind of display... random or flashing LED's. If there's nothing in the display, other (maybe fixable) problems could exist.

If you're not familiar with fixing these, have someone else take a look. I don't have the experience that Randy and Tony and others have, but I'm not too shabby, and I'd be happy to take a look at them for free. Don't know how close we are... you list Iowa, and I'm in Omaha. All I can promise is that they won't be returned working less well than they are now <grin>.

The HP-25 was truly my first love; I get great satisfaction in making them intact again.


Hey, thanks for the offer. It would be great to find out just what the problem is. I am not experienced/familiar with the testing or repair of these things. I did take it apart and there appears to be no PCB corrosion. However, there looks to be some minor (I hope) battery terminal corrosion. One of the old batteries that was in it had a very slight leak. I have not supplied any power to it except for putting in fairly new, charged batteries.

Please send me an email to my forum address with your mailing address and I will send you one of the units to examine. Unfortunately, Omaha is a longer drive than I want to make for this.

Thanks again,

J Grim


You've got mail.


Thanks, Michael. I plan to send one of these to you soon. I will email you when I do. Thanks again, Michael.

J Grim


The HP-25 is generally much easier to fix than the 25C, BTW.



Michael, I sent you an email, but just in case you don't check it, I am sending my 25 to you at your office on Friday via USPS. You should have it early next week.

Thank you,

J Grim


The HP-25 you sent is, indeed, a pretty specimen. There was corrosion on both contacts, but the circuit board is remarkably and unusually clean. The keyboard is perfect. The display is the older type with squarer numbers and a "regular" decimal point, which I prefer.

Some cleaning with a dremel brush and re-soldering of the contacts, and your machine is alive-- running well and programming. (Sometimes the RAM is shot and they won't program). I polished it up and removed some tape residue, and it looks great.

I've put lithium cells in, and I, personally, would recommend never using the wall charger.

Another beautiful HP-25 is alive. I will contact you by e-mail. Now... let's see if we can get that 25C to work!


That's great! Thank you so much! I can't wait to get it back and put it to use.

Thanks again,

J Grim

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