Didn't expect everything would fall out when opening a cheap keyboard. A few keys were not working because the manufacturer decided to press the keyboard matrix onto the controler board with 2 screws and a plastic holder. The pins on the matrix didn't had a contact to the board.
Fixed that with a graphite pencil and a piece of paper. Applied a thin layer of graphite on the pins for a better conductivity. The folded paper is now stuck between the plastic holder to increace the presure of the matrix onto the controler. Cheap fix for a cheap keyboard. All the keys are working now.
Never used that keyboard it was in a box. I think it was a birthday present. And decided to give it to someone who asked me if I have a spare keyboard. But first I had to check if it was working. This photo was taken after opening the keyboard.