18aa367c_ooting_Sewing_Machine_Problems__Symptom
[Root Cause] Threading is not correct. Thread has a knot in it. Thread tension is too tight. Needle is bent or blunt or has a sharp eye. Needle is wrong size. Needle has been inserted wrong. Needle and thread does not match. Starting to stitch too fast. Thread take-up lever has not been threaded. [Corrective Action] Correctly thread machine. Remove knot. Correct thread tension. Replace needle. Replace needle with correct size. Properly insert needle. Start machine at a medium speed. Use proper thread or needle. Check threading order. [Symptom] 
Upper thread breaks.
Troubleshooting Sewing Machine Problems
Symptom