14X17 Cassettes Jam

My 14X17 cassettes jam almost every time I run them. Now the strange thing is it is only if there is an image on the plate. If I am running them to test it or to clean them, they never jam. I have had my serviceman here multiple times and he has replaced every part imaginable it seems and it never works. The repairman thinks he has fixed the issue because he only runs the cassettes with no image on them. It's strange!