Assembled Battery-back port module repair kit for the often damaged flexible PCB in the battery bay (and I/O ports) of the HP-41c range of calculators.

This is the FLAT version, when the screw head domes are broken and grinded down - see pictures.

It is made of a flexible circuit, already collated to an 3D-printed battery-expansion ports module, ready for assembly within your HP41c. Standard colour of the base is black, but it can also be ordered in white (like the pictures)

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.

We assume that the screw supports are broken. Grind down to flat the screw supports with a dremel-like machine with some grinder head.

Once the backside is clean and free, glue the lower side of tthe module with E6000 glue, including putting some in the holes where the tabs are going to be. Then insert the module 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, and put pressure on the sides with cloth pegs to ensure good contact. Put also the module in to ensure good vertical position. Leave it overnight.

Reassembling

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 !!

This piece is for repair of HP41c full nut calculator, substituting the damaged or corroded zebra connector that links the main board with the processor circuit. New design in a single piece, with 50 times more conductivity than elastomeric contacts.

Installation instructions

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 processor.

There are two possible cases:

• In the old calculators the processor circuit is pressed down to the main circuit by a couple of nuts screwed on the plastic posts. The post do not have any thread themselves - the thread is carved by the nut itself. These have to be removed with care because you risk to break the post, by unscrewing counterclockwise. More than a couple of in and outs and the post will break for sure. Once done, lif the circuit. 
• In the newer ones, this pressure is exerted by two cylinders around the screw holes in the back side of the case. These are not present in the old models. You just need to lift the circuit.

Once the circuit is lifted, you will see the zebra connectors. These may be of three different types (thanks to monte Dalrymple for the image)

• The left one can be reused if treated with care and not corroded - clean it with paper embedded in Caig Deoxit. However, it doesn't work in some circumstances and there is no clear reason why.
• The second is completely useless and will need to be replaced. Every time.
• The thirs type is the best of the lot and can be reused with care if not corroded. It is also sensitive to friction and can be easily damaged. Discard if corroded.

Reassembling - closing the calculator

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!!

B-Stock: small scratch(es) on bezel. Perfect keyboard. 20% discount on the price of the Enhanced version. 

HP15c CE including Overlay 16c, Firmware change and Programming cable to avoid the DEC bug in HP16c feature

Includes:

• HP15c Collectors Edition
• Overlay 16c for the NOMAS 16c feature
• Patching firmware to avoid the DEC bug in NOMAS 16c feature
• debouncing increased to 100ms
• Programming Cable