How many HP-25Cs have we lost?

[John Garza (3665)]

I get so sad when I browse eBay and see all those non calculator specialists (online junk sellers) that have a 25C with dead batteries and plug in the charger and then sell it for parts because of the 'funny display'. These people are killing the remaining 25Cs ! In fact, most woodstocks on eBay these days are sold for parts. 15 years or so ago, there were still working units for sale.

[Maximilian Hohmann]

Hello!

(01-21-2023 02:15 PM)John Garza (3665) Wrote:  I get so sad when I browse eBay and see all those non calculator specialists (online junk sellers) that have a 25C with dead batteries and plug in the charger and then sell it for parts because of the 'funny display'.

I get even sadder when I talk to people and mention that I collect old calculators, only to hear "Oh, I didn't know anybody could be interested in these, not long ago I threw a couple of them in the bin!". Happend several times already. And therefore I guess that more HP-25Cs get lost by being thrown away, without even trying to get them working, than those who were destroyed by actually trying them out using the wrong method...

(01-21-2023 02:15 PM)John Garza (3665) Wrote:  In fact, most woodstocks on eBay these days are sold for parts. 15 years or so ago, there were still working units for sale.

Just did a quick search on eBay here in Germany and found two working ones (a more refinded search might find additional ones). But with three-figure price tags and no 25C among them.

Regards
Max

[Thomas Klemm]

(01-21-2023 02:15 PM)John Garza (3665) Wrote:  see all those non calculator specialists (online junk sellers) that have a 25C with dead batteries and plug in the charger

It also happened to participants of this forum:

Quote:Since I've fried a 25C the same way once, I'd call me ignorant as well until then.

[Maximilian Hohmann]

Hello!

(01-21-2023 05:59 PM)Thomas Klemm Wrote:  It also happened to participants of this forum.

When I found my first "Woodstock", an HP-25, on the flea market some 20 years ago, I was lucky because it came without a charger. Although I was already a registered member of this forum then, I had not yet come across the warnings regarding charging these without a battery. Maybe there weren't as many warnings on the forum back than compared to the last years. And because I had never encountered this issue with any other calculator I would probably have plugged in the calculator the very minute I came back from the flea market...

It is absolutely not the fault of the people who destroy Woodstocks by charging them without a battery (or with a bad battery in place), but entirely the fault of HP for designing such crap charging circuits. With every calculator that came before and most calculators that came after they demonstrated that they can do better.

Regards
Max

[Steve Simpkin]

My HP-25 was my first HP. It worked so well that I used it as my only calculator for almost 10 years. That said, the battery charger design was an extremely poor choice and I was very lucky that the combination of ancient batteries and the charger didn’t kill mine. i switched to using alkaline batteries after about 8 years when the NiCads no longer held a charge. It still works great.

[lrdheat]

I have a 25. Pristine except that I would have to get rid of light corrosion on the contacts that used to connect to the charger. How do I convert it to alkaline batteries?

On a similar topic, is there a way to do this with an HP 35 that is pristine, works wonderfully on it’s original wall plug?

[lrdheat]

The 25 is one I used in ~1976 in meteorology related work. The 35 was almost never used by my dad who purchased it in 1973. He wisely took out the rechargeable battery, and there is no corrosion in the battery area. He packed it away, it was given to me more than 30 years later.

[Steve Simpkin]

(01-21-2023 09:36 PM)lrdheat Wrote:  I have a 25. Pristine except that I would have to get rid of light corrosion on the contacts that used to connect to the charger. How do I convert it to alkaline batteries?

On a similar topic, is there a way to do this with an HP 35 that is pristine, works wonderfully on it’s original wall plug?

Here is an example of my HP-25 battery pack conversion to use alkaline batteries.
https://www.hpmuseum.org/forum/thread-18...#pid162675

For the HP classic models like the HP-35, several people make replacement battery packs that accept standard AAA batteries (alkaline or rechargeable). Search for the term "Rechargeable HP Calculator Battery Classic CASE HP 35, 45, 55, 65, 67, 80" for an example.

[Jonas Sandstedt]

Hello,
I would like to share a little story about HP-25.
A couple of years ago Panamatik launched the low power circuits for HP-34C and HP-25. I own an HP-34C and was tempted to convert it, but there was one problem -the HP-34C is fully functional, so I decided to keep it in original state. I liked the Woodstock design and started looking for a broken HP-25 that I could convert instead, and found one for about 35 Euro, it was sold “as is” and “for parts”, lacking both charger and battery door/compartment. A friend helped me to 3D-print a battery door/compartment, and the calculator, that turned out to be an HP-25C, worked as a charm with new batteries. The same reasoning applied here, I decided to keep it in original state.
I kept looking, and now there was a picture of an HP-25 with battery door/compartment removed (lying beside the calculator) and charger connected, the calculator showing only zeroes. Yes, I thought, this must be broken and was mine for 25 Euro. When I received it, I put in batteries and I think you guessed – it works as a charm. Having an HP-25 that work as well, I decided to keep it in original state also.
This was 2 years ago, and these calculators still work. Since then I have not found any more broken HP-25s for such a fair price, so I have not yet bought anything from Panamatik. But I keep my hope up. (I have one broken HP-19C, but to my knowledge there are no repair circuits available – yet.)
Best regards Jonas

[John Garza (3665)]

I was in a similar position, All my 25C's work and I was reluctant to sacrifice one for the Panamatik upgrade. I did have a 67 with a main logic board problem so I opted for a teenix replacement. Works great.

As for power, I just remove the center plastic bar in the battery pack with an Xacto knife and I can slide in AA Alkaline or rechargeable batteries then install the battery pack in the calculator as designed. For rechargeable charging, I always remove the battery pack and use the external woodstock recharger cradle. If you don't have one, it would be pretty easy to make.

-John

[teenix]

(01-23-2023 06:14 PM)Jonas Sandstedt Wrote:  (I have one broken HP-19C, but to my knowledge there are no repair circuits available – yet.)
Best regards Jonas

Work in progress :-)

cheers

Tony

[Jonas Sandstedt]

That is really interesting Tony!
Please post updates on this work if you have the opportunity. Do you have a working 19C to use for the development?
Best regards Jonas

[teenix]

(01-24-2023 02:01 PM)Jonas Sandstedt Wrote:  That is really interesting Tony!
Please post updates on this work if you have the opportunity. Do you have a working 19C to use for the development?
Best regards Jonas

I'll do my best :-) I started the code for it the other day. I sourced the necessary IC's so hopefully it will make a debut sooner rather than later. As I have also managed to source the parts for the Spice project, I hope to have a completed model working early next week.

I am lucky to have a 19C which is not functioning properly on loan from a generous Forum member while I develop it. Perhaps in the future, I will find a suitable one for myself

cheers

Tony

[waspentalive]

I have an HP25 that seems to have a problem, I had replaced the Nicad batteries and it was working, but then one day it displayed only a "1". Now it won't power on at all. I have an HP-specific charger that fits the connector at the top of the calculator, and I tried charging it. No help. I have also tried taking out the nicads and putting normal AA cells - same behavior.

Is this the "Lost" failure mode you have been talking about?

Is there a fix? Can I easily repair my calculator? I do not feel technically capable of soldering inside something like my HP25 so if the fix is hardware, I will have to seek help.

[John Garza (3665)]

(12-11-2023 03:28 AM)waspentalive Wrote:  I have an HP25 that seems to have a problem, I had replaced the Nicad batteries and it was working, but then one day it displayed only a "1". Now it won't power on at all. I have an HP-specific charger that fits the connector at the top of the calculator, and I tried charging it. No help. I have also tried taking out the nicads and putting normal AA cells - same behavior.

Is this the "Lost" failure mode you have been talking about?

Is there a fix? Can I easily repair my calculator? I do not feel technically capable of soldering inside something like my HP25 so if the fix is hardware, I will have to seek help.

First, scrub the battery contact posts in the battery well. Ensure there is zero corrosion/contamination. And wipe the contact points on the batteries as well, and ensure the battery dual spring in the back of the battery pack is corrosion free and conducting. With the battery pack assembled, check it on a voltmeter. Should be 2.5V to 3V depending on charge and what batteries you are using.

If all that is good, you may well have a dead machine. The Panamatik upgrade is the preferred option (the other being cannibalizing chips from a donor machine.) Either way it involves de-soldering/soldering.

-J