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.
Product no.: zebraholder
Zebra Holder to keep the elastomeric zebra connectors in the contacts between main board and processor circuit in the HP41c calculator family, full nut versions.
Product no.: lowerscrewblack
Two long screw for the lower screw posts of HP41c calculators - black