Topic: HP 25 charger question

Hello guys,

I'm new to this forum and this is my first posting. Thanks to Jacques for adding me!
I have a little HP calcs collection and among them is my only Woodstock series calc, a HP 25 (unfortunately, not a 25C).

Quite normal, I'm having problems with the power supply. I do have the 82024A charger (it's the version with an applied sticker, so apparently a Classic series charger) and it does output the ~10V AC.
The calculator itself works fine (all keys, all digits) when I connect power from my lab power supply (2.8V DC) directly at the battery connectors. I did have heavy corrosion, though, (leaked very old rechargeable batteries from the person who sold it) but was able to remove it with a little bit of vinegar. Here's a photo: http://f.cl.ly/items/3v0r3X2P0f2I1n3X3o03/IMG_6120.JPG

I do have a battery pack "shell" and put two sully charged NiMH 1.2V rechargeable batteries in. Looks like this: http://f.cl.ly/items/0H0k36111c1r2q1y152j/IMG_6119.JPG

But the 25 won't turn on with this battery pack installed. I suspect there's a simple contact problem. My DMM says the voltage from the accu pack is 2.79V.

Do you guys have any hints for me what I can try/do to make my 25 work again on batteries?
Plus: when I plug the charger into the 25 (with the battery pack not installed) I just get weird blinking digits in the display. What does that mean? Can't the 25 be used with the AC adapter only? Is it a must to have a rechargeable battery pack installed when using the AC adapter?

Hint: I' very interested in electronics -- but haven't studied it and am just learning. I do have an oscilloscope and stuff but am still in the beginnings of understanding circuits ... ;-)

Re: HP 25 charger question

Here are some close-up photos of the battery contacts:

http://f.cl.ly/items/1v3h1O3s2p1C0d3h2r1P/IMG_0007.JPG

http://f.cl.ly/items/1N1S0p3u0w042r3G321B/IMG_0005.JPG

Re: HP 25 charger question

Oh, and this little metal clip that can be see on the photo of the battery pack in the first posting is something I made in an attempt to increase contact ... ;-)

Re: HP 25 charger question

Stefan,
See this page on the site:
http://www.jacques-laporte.org/Woodstock/ws_HW_main.htm
and watch the video.


I just get weird blinking digits in the display. What does that mean? Can't the 25 be used with the AC adapter only? Is it a must to have a rechargeable battery pack installed when using the AC adapter?

The flickering display is the sign of a high voltage (> 5dc) applied to the micro controler ACT.
This situation might cause permanent damage to the RAM or ACT.
The circuit via the Nicad is open.
Try to remove the corrosion on the 2 battery's tabs

Take care,
Jacques.

Re: HP 25 charger question

Thanks a lot, Jacques!
I'm happy to report that my HP-25 is working with a battery pack again! :-)