hp41c corrosion

Corroded Battery contacts

Instructions for battery and ports module

Open the calculator

First remove the rubber feet. To do so, use a small, flat screwdriver and introduce it beneath the rubber, taking care of pulling also the adhesive sheet that glues the rubber to the calculator. Try to make here a good job because usually you will have to reuse the rubber feet when you're done. Put the rubber feet aside so that they don't hinder the work (they have an uncanny ability to adhere to shirts, tools, calculators and eventually get lost.

Unscrew carefully and slowly the four screws beneath the rubber feet. Turn gently the screws: they operate on plastic that, after 30 years, is very brittle and fragile. It is very easy to break a screw post or "overdo" the thread.

Remove the back side of the calculator and put it aside. For comfort, remove also the intermediate piece between backside and main body. Later we will take care of putting it the right way, since it has two ways.

Remove the old piece

Now it is the time to remove the damaged battery-ports module. To do that, first remove all 4 module covers or modules; then pull the module vertically and carefully, since there are four plastic tabs in the calculator used to secure it, and it you do horizontal movements you can bend or break them. Yes, they have also became brittle!

Sometimes grit and grease have "glued" the old piece to the backside. It will be very difficult to remove it. Be aware that it is NOT glued by design - this is an unwanted effect of grease, grit and time. To remove the piece in this case, try pushing up with a screwdriver on the back module connectors. Increase upward force until eventually it separates from the body. Clean the backside plastic with water and soap or a lenses cleaner. It may happen that one or both of the screw supports are broken. You will have to repair it beforehand with the broken back repair piece.

Once the backside is clean and free from the old battery module, insert the new one carefully, making sure that the 4 vertical tabs are not bent. This is done without the module covers in. Be sure that it goes down to the calculator body. 

After it has been installed, put the module covers or modules so that they push the piece in place.


You can now reassemble the calculator. Put the keyboard face down on the table. Then, put the intermediate piece with the open side upwards, taking care that the wider part is up, like "opening up"  (this piece has a slight angle when looked from the front of the open side). This is important for the calculator to close properly. See picture.

Then put the back side on top. You can start by any screw - I usually start by the upper ones. If everything is ok, you will be able to screw through the piece and into the calculator. Screw carefully not to break the threads. If that happens, repair will be substantially more complex and will need the upper post repair piece and some drilling.

And that's it!!


Please be sure to eliminate rusting from the main board with Caig DeOxit (best), WD-40 (not as good) or other suitable cleaner, applied with cotton buds.

Save your HP41c !!


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New Repair kit for HP-41c battery bay and expansion ports

Product no.: Flex-PCB

Adhesive circuit for the often damaged flexible PCB in the battery bay (and I/O ports) of the HP-41c range of calculators. Shipping included in price.

26.00 *
In stock

Assembled HP-41c battery bay and expansion ports module

Product no.: Flex-PCB Assembled

Assembled module for the often damaged flexible PCB in the battery bay (and I/O ports) of the HP-41c range of calculators. Shipping included in price for EU customers.

New price: cheaper circuit translating to 10% lower price!

55.00 *
In stock
* Prices include VAT