Brother CB3-B917 Service Manual page 53

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