HP 41C series battery issues

[Seisland]

Hi, I'm wondering if anyone has heard of this problem. i have a 41CV and a 41C. I replaced the "N" batteries in the C but it wouldn't turn on despite new batteries. A month later the same thing happened to the CV. I went as far as buying batteries from another place just for comparison but got the same outcome. The contact points don't look corroded or dirty on either calculator. I'm puzzled. If anyone has any suggestions I'd be interested in hearing from you. Thanks

Ed

[Craig Bladow]

You have undoubtedly checked the battery orientation a number of times, however the only times I've experienced this issue is when I installed a battery with the wrong orientation. You don't happen to have an IR module and an IL module installed at the same time?

[GreyUser]

Corrosion on the battery springs? It only takes a speck of green or blue and it’s a kaput calculator.

[mfleming]

Try measuring the voltage of the battery pack by placing a metal rule across the two inner batteries and your DVM leads on the outer two batteries to confirm that the calculator is being powered. If you read nothing, then have a look at the springs at the bottom of the battery case.

The top of each spring is pretty small in area and is sometimes tilted to the side enough that it does not touch the battery positive button. A bit of foil between battery and spring will help. I've also seen corrosion on the spring tip causing contact problems, and even a broken spring pair that fails to bridge two batteries together!

[Seisland]

I'm a bit embarrassed. It WAS the polarity. My other 41C's come with a battery pack so I forgot to put the N's in proper sequence. Thanks for reaching out

Ed

[Craig Bladow]

I'm glad you figured it out.

[Seisland]

I appreciate the help

[Andres]

IIRC HP-41C includes a diode in the CPU board to prevent damage to circuits due to errors in battery polarity. It is a Schottky diode, whose forward voltage drop is less than the forward voltage drop of an ordinary silicon diode, a not-so-usual and nice engineering detail.


DISCLAIMERS

Please disregard any idiomatic mistake. My imperfect command of the English language may prevent this message to convey its intended friendly content.

Please forgive any inaccuracy due to the fact that this post is based on 40 year-old memories and is not based in current and verified research.

[Wes Loewer]

(06-20-2020 01:37 PM)Andres Wrote:  IIRC HP-41C includes a diode in the CPU board to prevent damage to circuits due to errors in battery polarity.

This reminds me of an incident that happened around 1986 or 87. I was a graduate student at Texas A&M and there was an hp dealer just off campus. My 41cx was behaving strangely so I brought it to the shop when there were a couple of guys from HP who were there for some promotional event. I showed it to them and mentioned that the coat I carried it in often generated static electricity when I put the coat on or off. One of the guys took the calculator and said "don't tell anybody I'm doing this" and proceeded to remove the batteries and put them back in with the polarity reversed. When I expressed my "concern" he assured me that it would be okay. He left them in for a short while and then reversed them again back to their correct polarity. Sure enough, when he turned the calculator on everything worked fine. He said that the 41's were susceptible to static and reversing the batteries cleared the problem.

I'm not recommending that anybody try this, but that's what happened. But now it makes me wonder: Since there is a diode, what good did reversing the polarity actually do?

[Erik-M]

Every diode has leakage so there is always a few uA when you connect the batteries reversed.
Depending on the diode type even shortening the terminals work for draining the capacitors in the calculator. I know shortening works for example for the HP15C but not for the 41, I guess different diodes with different leakage current. Reversing the batteries in the 41 drains the capacitor faster but may be risky when you let them in for long. I would never do this.

[JurgenRo]

(06-18-2020 12:15 AM)Seisland Wrote:  Hi, I'm wondering if anyone has heard of this problem. i have a 41CV and a 41C. I replaced the "N" batteries in the C but it wouldn't turn on despite new batteries. A month later the same thing happened to the CV. I went as far as buying batteries from another place just for comparison but got the same outcome. The contact points don't look corroded or dirty on either calculator. I'm puzzled. If anyone has any suggestions I'd be interested in hearing from you. Thanks

Ed

That happens to me all the time. Usually it is sufficient to wait some time between changing the battery and turning on the computer (I have no idea if there is a physical explanation for this behavior, though). Sometimes it helps to carefully twist the computer slightly around its longitudinal axis.
Regards
Juergen

[GreyUser]

The reversed battery trick works best with fullnuts and can most times allow recovery without the loss of memory. If that fails, a hard reset will always recover a locked up unit.

Locked up halfnuts are usually only recoverable with a hard reset and many times reversed batteries are the reason for the lockup. Of course YMMV.

Hard reset: Hold down the backspace key while turning on. See the MEMORY LOST message and it’s running. Without any previous programs