READ IT CAREFULLY, PLEASE!
THE PROCEDURE BELOW SHOULD NOT BE PERFORMED IF YOU HAVE ANY DOUBTS ABOUT HOW TO DO IT. PLEASE, ASSUME YOUR OWN RISK AND TRY THE EXPERIMENT IN SOME OTHER DISPOSABLE MATERIAL BEFORE TRYING IN YOUR CALCULATOR. I ALSO SUGGEST WAITING FOR SOME OTHER SOLUTIONS.
I have once tried, with success, an epoxy cement to fill-in the defective thread (here in Brazil we have a so-called Durepoxy; I'm not sure this is the same you will find in Croatia). Try this:
- Open the calculator, remove the motherboard, I/O battery contacts assy, battery holder and screws and keep them in a safe place.
- Mix a bit of both parts of the epoxy cement and fill in the defect thread.
- Before the epoxy cement dries out (try sensing with your finger), you should insert the screw with the screw driver carefully, so it will rebuilt the thread (I have 'moistened' the screw with liquid soap and dried it out with a hair drier before insertion, so it would have a thin soap layer to avoid the epoxy cement to mess around the screw itself).
- Wait for one-two minutes and unscrew it with the same care you had to screw it in.
Then its just wait till the epoxy is dried.
This procedure worked fine for me. If there is another, better solution, please let me also know about it.
You will need special care with the epoxy cement so it will not smear over the keyboard's back side.
Good luck.