If the problem is not with the free feeding of paper from the roll, it is probably something to do with the feed motor or its drivetrain. Try a different roll of paper first and if you get the same performance I would suggest getting an external printer (seiko, martel, etc) and using it if you wish to keep using the PTB for scored races. Usually repairs of this type of thing are far more expensive, if available at all, than using an off the shelf external printer.
An external printer will require some programming to get it going. If you are interested in this option I can quote you a price for a pre-configured printer that will be plug and play with your PTB.