This is a must-see video if you've ever been curious how a punch card machine works:
This one is from The Answer Lady - thanks, Kathryn & Jack Doubrley, for this very interesting look inside the machine.
Caution: As you watch this, you'll hear Jack warn you more than once that you would not want to take your machine apart yourself. It sounds like great advice to me! We do have a few terrific repair businesses in the machine knitting community, and I recommend you use one of the professionals when you have mechanical problems.