When I am having machine problems the first thing I do is remove the spool of thread, remove bobbin, remove bobbin case holder and remove needle. Then I clean the machine, replace everything and put in new needle. This works for me. As a former dealer the main thing I found causing machine problems was dirt, dust, needing oil, needle in backwards, and threaded wrong. Believe it or not but long ago the sew machine repairmen made housecalls. One of the service calls was due to it not being plugged in to the outlet.