sewing machine hand wheel stuck
I teach high school Home Ec and am currently teaching a unit in sewing. I have several Bernina 801 Sport sewing machines. The problem I am having is that the hand wheel on some machine are stuck and won’t budge, which makes them unusable. I’ve dealt with stuck/jammed hand wheels before and have been successful in fixing them by removing caught thread, wiggling knob and hand wheel, tightening knob, oiling parts, removing needle, etc. I can not figure out how to get the hand wheel moving again. Looking inside the machine, it appears that some of the plastic “gears” are stuck. If anyone has any suggestions that would help solve this problem, I would greatly appreciate it. Thank you.