HP Forum Archive 06

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HP-25 battery Message #1 Posted by Seth on 13 Nov 2001, 11:06 p.m. I just received a HP-25 with no battery. It has the battery cover/case with the spring and + and - inked on it. I tried plugging in some AA batteries, and with some creative wiring to get it to connect to the terminal, it still didn't work. Anything that I'm missing?

Re: HP-25 battery Message #2 Posted by Michael Meyer, M.D. on 14 Nov 2001, 12:18 a.m., in response to message #1 by Seth Seth, Getting good battery contact in the Woodstock series calculators can be tricky. Sometime I put a drop of solder on the negative side of the battery so it will stick out as far as the nipple on the positive cell. Also, make sure that the spring is well polished or sanded if you haven't wired the ends of the batteries together on the spring side. The first step, however, is to see if the calculator has "life". Take two cells already together, in a battery holder case (or a regulated power supply, if you have one, set to 2.4 volts. I have lithium AA cells in my every-day HP-25 that have lasted for months, will store safely for over ten years, and won't leak. They do put out about 3 volts, which can be a little hard on the circuits, so I'm told. I've had no problem with this, and the calculator never needs to be charged.) Hook up some test leads (alligator clips) to the batteries. With the bottom of the calculator facing up, the positive terminal is on the right (the wider side of the calculator). Hook up the power with tight clips, and wiggle them a little bit for better contact. Try the calculator. If nothing comes on, you have much more restoration to do, if restoration is possible. You can try to carefully sand the terminals with a dremel tool and try the external supply again. If the calculator works with the external supply, then you need to work on making sure the battery pack makes contact when the springs are extended in the case. Thus, my luck with a small ball of solder on the negative battery face. Tighten the springs, also, by stretching them some. Let us know how it turns out!! The HP-25 was my first true love. I've never known any other machine so well. If it says "Meyer" on it, it was the one stolen from my locker in high school. Just kidding. Good luck! Michael

Re: HP-25 battery Message #3 Posted by Seth on 14 Nov 2001, 2:37 p.m., in response to message #2 by Michael Meyer, M.D. I can get the calculator to turn on now (sometimes), and there is 0 in the far right side. No button presses change it. I tried turning it off and on, then I get a 0 in the middle, right about where the GTO button is. That doesn't seem right. However, the 0 is still stuck on there. The PRGM/RUN switch is in run.

Re: HP-25 battery Message #4 Posted by David Smith on 14 Nov 2001, 4:53 p.m., in response to message #1 by Seth My favorite way (recommended to me by HP in the dark ages) to get good contacts on Woodstock, HP19C and HP10 machines is to make a small folded square of about three layers of aluminum foil and place one over each battery contact in the battery pack. Insert the pack into the machine and voila... works every time for me. HP made Woodstock battery packs in two different ways. In one type of pack the cells are not joined together except by the spring. This allows the cells to float around and make contact to the calculator pins if they are uneven. It also caused the cells to not make good contact with the spring. The other type of packs strapped the cells together with a weld strap. This type of pack did not have the problem with bad contacts at the spring... it did cause bad contacts at the calculator if the calculator contacts were not even (usually the case). Aluminum foil is your Woodstock's best friend... If you need to rebuild a Woodstock pack and are not sure of the battery polarity you can find it marked inside the battery holder (a small raised outline of the battery) As far as the single "0" roaming around your display... sounds like a bad chip. 90% chance it is the ACT chip (the large 22 pin one).

Re: HP-25 battery Message #5 Posted by Andrés C. Rodríguez (Argentina) on 15 Nov 2001, 10:01 p.m., in response to message #4 by David Smith Please don't ever think about running your HP 25 from an AC Adapter if you are not 100% sure that GOOD rechargeable batteries are in place and doing GOOD contact with the calculator terminals! Else, you may irreparably damage your calculator. There have been many postings about this situation here at the MoHPC Forum, you may search for more detailed ones. Running from 2 Alkaline AA is acceptable, even with a little higher voltage than NiCd (many people reported this OK, but, as always, NO WARRANTIES!!)

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