Brother International CB3-B917 Service Manual - Page 53

6.TROUBLESHOOTING Problem 12. Final stitch skips Cause Looper misses thread. Solution Refer to "11.Stitches skip at sewing start" . Page 46 631s • Occurs together with thread cutter errors. • Stitch comes out when the material is removed from the machine. 13. Thread cutter errors (B917A) Approx. 20 mm Approx. 20 mm Link skipped Approx. 45 mm Link skipped Thread cut cleanly Thread cut cleanly (4-hole) 632s 633s (2-hole) Movable knife misses thread. Delay thread trimming timing. Needle thread is short Thread cut cleanly 634s 18 36 0.5 mm 627s Movable knife and fixed knife do not cut Replace the movable knife. 21 properly. Sharpen or replace the fixed knife. 22 Improper movable knife position (1) Check the fixed knife position. 21 Fixed knife 35 635s • Looper catches thread normally in stop position. • Stitches are properly formed. Approx. 2 mm 331s (2) Move the movable knife away from the looper. 22 0.5 - 1 mm 36 Movable knife 636s Movable knife misses thread due to Adjust so the vertical feed cam mark is aligned 30 machine stop feed assembly position. with the cam positioning pin when in the stop 39 • If the thread position. does not cross when sewing 4-hole buttons. 637s • Occurs when sewing the first half of the button. 14. Thread cutter Insufficient thread tension when final (1) Increase tension at main tension. 40 miss (B916A) stitch is tightened. 635s (2) Increase thread tension. 638s • Looper catches thread normally in stop position. • Stitches are properly formed. Insufficient tightening of final stitch. 615s (1) Check button clamp lift stroke. 13 - 14 mm 648s (2) Decrease brake strength. 47 CB3-B916A/B917A