First, you need the service manual. Second, a good quality screwdriver set so you don't strip any screws. Chapman makes a good set. After reading the manual and removing the bottom stand and arm cover you will see the gears that can be adjusted to correct the timing issues. once that is put back together you will need to remove the top and side cover to reveal the workings up top where you have thread tangled/stuck. Once that area is cleaned up, you will have a very nice machine that works excellent. The service manual is available for free on line if you google it. Take your time. Its not too difficult to repair yourself if your mechanically inclined.
fixedmypfafftoo, June 2015