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.
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.
Now you have to lay the new zebra. As it is simmetrical, it works all 4 ways. Make sure it goes to the end of the tubes on both sides. All circuit lanes should line up perfectly with the circuit pad below. Once laid down the zebra, put the processor circuit on top and press down to ensure contact.
For the cases where there were nuts, we recommend not using the nuts anymore and replace them by one of our spacers. You can try several height measures until you find the one that closes perfectly the calculator and yet pushes down the circuit to ensure good contact.
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!!