Slipping magnetic cards

[AndiGer]

Thanks for the advices. Also the pencil rubber didn't change the behaviour.
Came to the idea to try in the HP-41 card reader. After I got checksum error there I decised to add the clipped corners and rewrite the cards. That finally did the job :-)
Somehow the 97/67 readers seem to have also some logic when to stop the motor running depending on the card read successfully?
After writing the before malfunctioning card with motor acceleration it now works like a charm.
Andi