Dead HP41CX?


I just acquired an HP41CX complete with a dead rechargable battery packs. I pluged the unit in and pressed the ON button, but nothing happened. Is my calculator dead? Is there some secret handshake to bring it back to life?

When the battery pack is plugged in to the wall charger, the measured voltage on the battery pack is about 5.1 volts. This makes me think that even with the dead battery, the wall charger should be powering the calculator. Since it is not, I presume the calculator is dead.

One last hope would be to buy 4 N-sized alkaline batteries and see what happens. Is that worth a try, or would I be throwing my money away?

It would be a shame if the thing is dead. It came with a soft brown case, a printer, two card readers,MATH 1, SURVEYING 1, and XMEMORY.

The calculator also came with a black sliding clamp with a spring on it. It says "PRIMA TOOLING PTY. LTD. MELB on it. It is 9 cm wide and 7.5 cm high. Evidently it is a stand to hold the calculator up at a 30 degree angle.



Is my calculator dead?

I would take a look at the battery contacts first, before declaring the poor thing dead! With old/dead recharchable batteries, there is often some leakage of electrolyte that will affect the battery contacts.

Be very careful when cleaning them, because they are made of nothing but flexible plastic/copper circuit boards (maybe the worst sin HP ever commited?). Use absolutely no abrasives, only some alcohol or special cleaning fluid ("contact spray").

Good luck,


If you can't get it going, can. They fix only discontinued HP calculators, and it sounds like they do an excellent job. I have no experience with them (as fortunately my old HPs have continued to work perfectly) but many on this forum have spoken highly about .



Most problems with not working 41's are caused by corosion of the middel contactbar or by a cracked shell. If the screwing posts (under the rubber feet) cracks, there is not enough pressure to make good contact between the keyboard-PCB and the battery/ flex-pcb and between the keyboard-PCB and the logic-PCB. Repairing the post's with some good glue can fix you problem. If there is corosion damage you have change the flex PCB and clean the calculator. Viktor T. Toth wrote a nice article about corosion. You can remove traces of corosion with cleaning fluids like iso-propanol or cleaning vinager.

Regards, Rik


Hi Gordon,

It's (remotely) possible that your really dead rechargables are shunting so much current that when you attempt to run your calculator, the little rectifier in the battery pack is unable to supply enough current to charge the cells and run the machine, so the output voltage is swamped. Try this: leave the battery pack plugged into the charger for a few hours, then unplug the charger from it and check the voltage. This should tell you if it has any life at all. If your rechargable pack proves dead, it would indeed be worth it to try a set of N-cells in the machine (do you have the N-cell battery holder?...the rechargable pack won't work with the N-cells).

Good luck and best regards, Hal


Hal, your suggestion seems to be a winner. It appears that the old battery pack was unable to produce enough current.

I did as you suggested, and after leaving the battery pack plugged in for a few hours there was some limited success. Garbage characters appeared on the display, but they soon went away.

Then I tried unplugging the Math and the Surveying modules from the top of the unit. They must draw enough current to matter, because the calculator now is up and running with those items removed.

For my next trick, I followed a recommendation I found elsewhere and ordered 4 replacement NiCad cells to solder into the old battery pack. For about $23 is shipping to me a 4-cell pack of Sanyo 1/3AAA cells, with 1-inch tabs on the + and - terminals. I hope that will result in a fully functional HP41CX.


For my next trick, I followed a recommendation I found elsewhere and ordered 4 replacement NiCad cells to solder into the old battery pack. For about $23 is shipping to me a 4-cell pack of Sanyo 1/3AAA cells, with 1-inch tabs on the + and - terminals. I hope that will result in a fully functional HP41CX.

For what it's worth, I just ordered and received a set of four KAN 1/3AAA NiMH cells from
Cheap Battery Packs. These are the same size as the Sanyos, but with 160mAh capacity instead of 50mAh. I'll let everyone know how they work out. KAN is a well-respected brand in the electric model aircraft field.

I also ordered GP 4000mAh Sub-C cells for my HP-41C printer, and Elite 1700mAh AA cells for my newly acquired HP-67 (I chose the latter over the Sanyo Eneloops, my current favourite rechargeable, because of the lower internal resistance).



Stefan, if it works then that is a great source for battery packs. If I navigated their web site correctly, the 4-cell KAN160 pack is only $7 total. If this cell works in the calculator, it is 3 times the capacity for 1/3 the cost, for a 9:1 performance:price ratio!


I encountered a small problem replacing the batteries in my rechargeable battery pack. Thinking it would save me some work, I paid $4 extra to have the battery company build a 4-cell pack. That ended up being more work, because they built the pack by gluing the individual cells together before connecting their terminals. The resulting battery pack is too narrow to fit properly in the plastic battery case.

The original cells in the pack have some space between them, so much that the new 4-cell battery pack was only as wide as 3 of the original cells. That meant that the metal springs would not line up correctly with the cells.

I solved this problem by gluing a small block of wood to the side of the + terminal of my new battery pack. Then I routed the metal tab laterally from the + terminal of the battery pack, around the wooden block, and then back to the PC board of the rechargeable battery pack. The spacer makes everything line up correctly, so I have a working battery at last.

The next time I do this, I'll just order individual battery cells with tabs on them. I'll be able to solder them together with the proper spacing, and life will be much easier.

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