TROUBLE SHOOTING A SEWING MACHINE:
I Google searched and very quickly came up with lots of stuff - here are some to look at - maybe book mark for future reference:
http://sewandserge.com/tshoot.asp
http://www.buzzle.com/articles/troub...-machines.html
http://aces.nmsu.edu/pubs/_c/c-202.html
I know there are more out there. For about $10 each, I was able to invest in a SERVICE manual for each of my good machines. Some of the older machines have so much info you only need an operators manual so give your manual a good look see.