1. Fault characteristics: the bottom line cannot be drawn. Product reasons: The bobbin thread is too short, the bobbin thread is caught in the shuttle door, the needle is too high, and the bobbin cannot hook the thread loop.
2. Fault features: the needle bar moves. Product reasons: Needle bar hole, needle bar wear, needle bar connecting screw loose, needle bar displacement.
3. Fault characteristics: skip a stitch after several stitches. Product reasons: The shuttle is worn, the shuttle tip is too dull, the sewing machine needle is too high or too low.
4. Fault characteristics: continuous jumper or one stitch cannot be sewn. Product reason: The needle quality is poor or the needle is bent and the thread loop cannot be formed normally. The needle of the sewing machine is too high to hook the thread loop, and the three needles of the sewing material and the sewing machine are not properly matched. Long-term use of shuttle, swing bed and other parts are seriously worn or broken.
5. Fault characteristics: thin seam without jumper, thick seam jumper. Product reasons: Insufficient pressure on the presser foot, too thin sewing machine needles, serious wear on parts such as the thread hooking mechanism.
6. Fault characteristics: thick jumpers are stitched, and thin jumpers are stitched. Product reasons: The needle hole of the needle plate is too worn, the sewing machine needle is too thick, the bottom of the presser foot is worn, or the presser foot pressure is too small.
