Good day to you,
It may be something as simple as a scew come loose on the feeding cam which is underneath the fee dog, you will need to take of the bottom cover, tilt the machine backwards and check that the screws are loose, if they are you may need to move the feed dog forward or back bit by bit to get the feed right, failing that it could be a broken gear, if you contact tandtrepair.com you can download the complete worksheet for your model.
Ken
drivewithken@blueyonder.co.uk
October 2007