@dave_m and @daver2 Thank You for your replies.
There are no foam or rubber keypads. These switches working with this copper "tongues".
I got the following answer in an other forum (a german one and yes I used the Google translator. Sorry for this :-)):
"
I had to re-solder a few contacts on the...
Hi,
my first post in this forum and I hope I find someone who can help me :)
I have here a PET 2001-B-32 with the business keyboard installed. And with this keyboard I have a lot of trouble.
4-5 keys are not working. I cleaned them and tested them with a multimeter tool. I also build
a small...