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Thierry‘s HP-41 corner

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Thierry‘s HP-41 corner

Informations de contact, plan et itinéraire, formulaire de contact, heures d'ouverture, services, évaluations, photos, vidéos et annonces de Thierry‘s HP-41 corner, Boutique vintage, Colmar.

Réparation et réanimation, achat et vente de calculatrices scientifiques programmables HP-41C, HP-41CV, HP-41CX et leurs périphériques reconditionnées / d’occasion

25/07/2025

This blog is about the batteries of the Woodstock (HP-21, HP-22, HP-25, HP-25C, HP-27, and HP-29C) and the Spice (HP-31E, HP-32E, HP-33E, HP-33C, HP-34C, HP-37E, HP-38E, HP-38C) series:

First, one has to understand that the wall charger delivers a higher voltage, so that some current can flow into the batteries to charge these. Inside the aforementioned calculators, there is a diode to convert the AC from the charger into DC for the battery, and a current limiting resistor to prevent over-charging of the batteries. The batteries themselves act as voltage stabilizers, preventing the over-voltage from the charger to fry the calculator by absorbing the “too much” to charge themselves, and to heat up the current limiting the resistor otherwise. In case of a defective battery pack, or corroded battery contacts, when the voltage limiting function is not longer given, the over-voltage of the charger will inevitably damage the calculator’s integrated circuits. That’s why one should never plug in the charger and try to operate the calculator without a known working battery pack!

Second, even with a working battery pack, many experienced users advise that the batteries should be charged outside the calculator, to prevent any of the risks cited above and to reduce the thermal stress for the calculator’s ICs, due to the heat radiated by the current limiting resistor. Add the fact that after almost 50 years, none of the original battery packs is still working and a great number of original chargers is also out of order or lost, and the fiddling starts with cutting the original battery packs, forcing new cells inside, forcing them again out to charge them, and so on. This adds new risks like accidentally switching the polarity and all this improvising is far from being satisfying.

Thanks to a new technical partnership with a German maker, Thierry’s HP-41 Corner has the solution to everything and you can from now on not only order new battery packs with high quality cells (not the cheap Chinese stuff) for all Woodstock and Spice calculators, but also a well thought external USB charger which takes the Woodstock battery pack directly, and the Spice battery pack with a slide-in adapter. No more fiddling with single cells, no running to the garage to find the original charger, just plug it into a free USB port and wait until the LED goes off, indicating that your battery pack is fully and responsibly (taking care of the cells) charged.

And all that at reasonable prices:
- HP-Spice battery pack 24.75€
- HP-Woodstock battery pack 29.50€
- USB charger box for Woodstock and Spice battery packs, including the slide-in adapter 48.50€
(plus shipping)

Please message me to order.

And now, since a picture tells more than thousand words, have fun!

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29/06/2025

Remember last Wednesday when I wrote about the successful repair of a HP-38C in ugly state and shape？After it was known to be perfectly working, Thierry Larché asked me if it was possible to do something about its cosmetic condition. I had to tell him that I could not do anything about the deep scratches in the faceplate, but that I would try to care about everything else. In ever case, the result could not become worse than it actually was. So, I disassembled the calculator again, managed to make some chemical magic happen and finally, everything took a bath, rinsing in the ultrasound cleaner. While far from being "as new", there is a noticeable improvement in the cosmetic condition. Check out the before and after pictures with your own eyes!

25/06/2025

Some months ago, my friend Thierry Larché brought me a HP-38C in extremely bad shape, due to leaked batteries. The thin bonding wires between the small display PCB and the LED display itself were partly eaten up by the acid, leading to lots of missing segments. Thus, in a first step, I had to find another LED display. Patiently hunting on eBay, I could find a HP-37E with other problems but a with working display. So, the slaughter fest started last night: Unsoldering the working display from the 37E (24 pins), unsoldering the defective display from the 38C (again, 24 pins), soldering the working display into the 38C (you guess it, 24 pins)…
That was enough for yesterday, and I continued today. As usual, the battery contacts themselves could be salvaged through thorough cleaning with a glass fiber pencil. The PCB traces which act as connectors for the charger were cleaned in the same way and then tinned. But the flex PCB between the battery connector and the power supply board needed to be replaced by a classic tailor made wiring. Final assembly, testing ok. Now up to installing a new rechargeable battery pack and there is another Spice calculator alive!

09/06/2025

I had hoped to finish more repairs than that over the long Pentecostal weekend. But 2 magnetic card readers with issues in the electronics, besides the usual cleaning/friction wheel/clutch problems, were and are eating up many hours which never will appear on any invoice…
Nevertheless, I managed to finalize a huge repair of a HP-41CV (lower screw posts, battery/module connector, and the LCD plexiglass needed to be replaced). Although I didn’t promise anything since some more recent calculators weren’t made to be opened and to be serviced, the customer insisted to send me also his HP-32S2. And, guess what, I managed to open it, to replace the weak foam stripe from the keyboard contacts, and even to seal the housing again, afterwards.

05/06/2025

There are times when my day job doesn’t leave me enough free time and I’m running late with HP-41 repairs. Nevertheless, after receiving spare parts from the lovely José González Divasson and his thecalculatorstore.com in Barcelona, I decided to attack a HP-41CV which had been sent in from Kronberg/Germany.
The lower screw posts were fissured, thus the contact between the main board and the CPU board was only sporadic. Cut them off, excavated, cleaned, and glued the repair piece in place, masking the small holes in the pcb beforehand. Although José states that with the recommended longer screws, it should keep in place without glue, I remain more conservative about this.
Now, there was also a crack in the plexiglass above the LCD. How to fix that? Unsolder the LCD. Break the old glass properly out (it was initially glued) and clean the edges. Don’t use swear words. Do the same on an otherwise not repairable “cadaver” without breaking it. Don’t use swear words. Glue it in place in the other HP-41. Don’t use swear words. Let the glue dry overnight. Open a beer and make a post on Facebook…

02/06/2025

Unusual fault on a HP-82104A card reader: Inserting a card acts the head switch, Vbb goes up but Vss remains at 0V and thus, the motor driver is not activated. I like challenges like this, even if it requires disassembling everything and unsoldering the power supply module from the logic board to find a bad solder point…

22/05/2025

Dear HP-41 fans, please do not try to fix your calculator yourself if you don’t know exactly what to do.
The repair of this HP-41C below would have been at least 50% cheaper if it had been sent in before overheating and burning the battery connector, the insulation foil, and the back shell…

17/05/2025

Not pretty, but functional - and when the housing is closed, you can no longer see it... The battery and charging contacts on this HP-33e were completely eaten away. The conductor paths were restored with tinned copper foil. For the battery contacts I shortened spiral springs from the battery holder of the HP-41 and soldered them on. As the flexiboard was also pitted, I rebuilt the connections with conventional stranded copper wire.

17/05/2025

While the new silicone in the HP-82104A card reader’s vibration damper is hardening, let’s attack the HP-33E where corrosion has completely eaten the battery contacts…
-33E

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