Broken Lower Screw Post Repair
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.
Let's assume that both posts are broken or cracked. The effect of this cracking is that the screws do not do their job. Usually, using longer screws may help, but this typically is short lived since the cracks will continue downwards. Once the pressure between both halves is softened, the calculator doesn't work anymore. The solution is to repair the broken posts.
Old methods to repair broken post is to glue them (but this doesn't hold together too long) and to tie them down with very small gauge copper cable, applying pressure so that it holds together. This may solve some cases, but not when the screw path has been destroyed - maybe due to strong tightening of the screws.
Other repair methods have been proposed, including drilling down the screw and placing in its place a cylinder with screw path, glued in place. We tried this method but there was a problem: the torque used to screw resulted in cracked glue and the cylinder separating from the substrate - every time.
Our method was devised with three goals in mind:
The piece that we have designed requires drilling the old posts to the keyboard ciruit level, taking care of leaving the hole clear. The design on the piece is such that the pin will be glued to the inner part of the rest of the screw post; and the surface of the piece can be glued to the keyboard circuit, so that the torque on the substrate is avoided (it also helps that torque is also resisted by the other post, when using the full piece)
When gluing the piece, there are several precautions that need to be taken:
We recommend to repair both posts at the same time. However, if you are confident on the resistence of the other post, you can cut the piece in two. As it is symmetrical, it can be used for both posts, just twisting it 180º. Using the full piece, the other post side does not need to be glued - the torque resistence is done by the post itself over a much longer distance.
Product no.: Lower Post Repair Kit
Set of pieces needed to repair successfully the lower posts of HP41C, 41CV and 41CX full nut calculators, including zebra connectors, lower post part, and keyboard support for clothes' pegs to protect the keyboard
Old price 70.00 €
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