Rebuilding HP41C and 82143A posts, OOPS and other (good) stuff



I have seen many people in trouble with the HP41 posts and consequent bad contacts, MEMORY LOST and all sort of malfunctions. A few days ago I tried a "new" method when one post definitely broke in many pieces. After getting into panic and restoring my temper, I put my brain to work and it worked, believe me! I had an idea: rebuild the post instead of restoring the broken one.

I dig a bit of my old stuff and found some styrene trees from old plastic models. I took the most resistant and cut a piece of it, the one with a diameter as close as to the original post. In the calculator I cleaned the surface where the post used to be and dig a hole exactly in the same place by using a small, sharp edged screw driver (you can use a better tool, of course), taking care to keep a small plastic ring around the hole. I worked a bit on styrene piece and made a recess in the edge, so it fit in the hole I dig. After cutting the styrene's opposite edge so it reached the original post's size, I used superglue to join the new post to the calculator and used a small modeler wrench to keep it in place. A few hours later I hand drilled (more precision) a small hole in the new post (styrene is somewhat soft) and force a new thread with the original screw and a screw driver. It worked perfectly. I rebuilt five posts in my calculators and today I rebuilt two posts in my 82143A. In the 82143A I also used metal sheets from old alkaline battery, folded as small tubes, to reinforce and keep in place the new styrene post I use to replace a broken one. It was too "tall".

Curiosity: there is an OOPS printed in the 82143A closed to the paper sensor. At the time I first saw this OOPS I could not understand why HP designers would write oops in the paper sensor... Aaah! Out-Of-Paper Sensor! Its O.O.P.S., for heaven's sake...

The good news is that I took some pictures of the rebuilding process (HP41 post only), step by step, but the (digital) camera I used is not mine, and my brother is sending these pictures back to me next week (maybe Wednesday). I'm not sure the pictures are good, mostly because the camera has no zoom lenses, I could not approach too much and used no support except my hands. I'm afraid they will give no good resolution, I cannot promise. If they are viewable, would you like them to be part of an article? I'll add specs like measurements and precautions.

Please, let me know what you think about it.

Oh, yes: I placed the contact leads in the correct position (Dam it!) and recovered the HP55 batteries: it is working perfectly. I used high-voltage capacitor discharge (about 310Vcc) to remove internal short circuit in the original battery pack. The batteries are charging normally.

I rebuilt two 82143A battery packs from three completely exhausted packs after applying this "dangerous" technique. The two remaining 82143A battery packs are working fine for about three months.

Today has been a good day. I think I can share these facts with you, mostly because some of you may be interested on recovering HP41 (and others) posts. About batteries, I can give more details. If this procedure is already known by someone that also knows disadvantages or dangerous consequences, please, reply this post before someone gets hurt or have his batteries damaged. If you have never done this sort of battery recovery before, please, do not try. I will not be responsible for consequential loss.



Hello Luiz,

of course I would like this post to become an article, so it does not dissapear. Even without the photos it could help. But it would be nice to see at least a photo of the "styrene trees". Since I am no model builder, I have none at home and must use something similar. :-)



The trees are what hold the plastic model parts. You know, you break the parts off the tree.

But, I would like more information on the battery pack recovery. What is the danger that's being referred to?

Thank you.



Yes, the trees are the plastic tubular shape "holders" that people usually throw away. I keep them for many reasons, and sometimes it is a lot usefull. Now more then nevr! And their tubular shape called my attention: I never thought about it before. I was affraid they could not hold the screw thread, but if you go with care, the thread holds it tight and firmly. If the thread looses, you can remove the post and rebuild it again.

I was once told that inverting polarities when submitting rechargeable batteries to high voltage may cause explosion and/or leakage. I though it would happen only if the high voltage is constant, not a pulse from charged capacitors, but as a precaution advice, it must be taken into account. I used the AC input capacitors and rectifier bridge from a disassembled PC power supply plus a regular 60W bulb lamp in series only to charge them (reduce peak current). I could recover about a dozen short-circuited rechargeable batteries, and definitely throw away some others.

I know it's risky, but I have some batteries working in my 82143 for almost three months and they are running fine.

Hope this is what you want.

The two points are:

1) if you use other plastic solvent instead of superglue, think that you should try it with matching plastics, say, try to use the same plastic used in the HP41C's case, so the solvent will melt and fuse the same material; I do not know what's gonna happen if plastics are different. As I do not have plastic solvent, I thought superglue a good choice, and it worked fine

2) I removed the keyboard so I could work with mre freedon: no keys to glue together, no contacts to care about... it's easier when the keyboard is already removed.

In fact, I have three fullnuts with the keyboard removed and the case screws are enought to keep them in place. I did not rebuild the plastic rivets. I think the Voyager's keyboards are a lot more complicated...

I hope this helps.




after wondering around some articles, I found this very important information. I must say I was not aware of this particular article from Steve (Australia) when I posted my own about batteries.

The information herein is a lot important and precise. Should anyone try to recover their calcualtor's rechargeable pack, do it.

It is important to know, also, that too old packs will not keep the same perfomance. In my particular case, after some charge/discharge periods (ouside and inside the calcualtor), the oroginal HP55 pack (about 18 y.o.) cannot hold the chronometer for more than 35 minutes ( display only). I am not sure about how long would the original, fully-charged pack hold it, but I think this is less time then it would if new.

Any additional information?



This technique for recovering nicads has been around for decades. It's most helpful on nicads that have seen few charge/discharge cycles but have internally shorted just the same. Cells that have had many change/discharge cycles can be recovered too, but the fix won't last long.

Steve's article recommends using a high voltage capacitor to do the trick, but I don't. You're much safer using a very large value, low voltage capacitor like the kind you'll find in old DC power supplies. Something about 50,000uf at 20 volts works well and is much safer.

The key to zapping old nicads is to feed in enough energy to break the short. Energy storage in a capacitor is given by volts^2 * capacitance so the high voltage. In Steve's example he was charging a 160uf capacitor to around 125 volts giving 2.5 joules. A 50,000uf capacitor charged to 15 volts will give 11.25 joules and although you'll get a bigger "bang" it's got little chance of hurting you. But keep in mind that you'll need to use much thicker wires between the capacitor and the nicad cells when you zap.



Thanks for the tips, Katie. I have a 40,000uF/70Vwv Siemens "oil-can" that will probably be charged soon...



You DO NOT break the parts off the tree. You clip it off, peroid. Otherwise you may damage the part you take off (part of the part left on the sprue (plastic tree)).

/Håkan (model builder :-)

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