Needle Thread Runout - Brother LH4-B800E Service Manual

5. Troubleshooting guide

5-8. Needle thread runout

Cause
Upper thread Upper thread trimmer
trimmer assembly position
assembly
Operating pressure of
upper thread trimmer
assembly
Upper thread trimmer
driving spring
Tension End of tension release
release at the beginning of
timing sewing
Opening amount of
zigzag tension discs
and bar tack tension
discs
Upper thread Needle thread take-up
feeding
5 - 8
Check
Move the setting plate
assembly to adjust the
scissors assembly
setting position.
(Upper thread scissors
longitudinal position
adjustment)
Upper thread scissors
cutting depth
adjustment
Correct operating
pressure by upper
thread upper trimmer
Change if transformed
Retard the tension
release timing
Adjust the release
dimension
Increase needle thread
take-up
Solution
Adjust the operating pressure as
follows; After thread trimming, pick
the pinched thread and shake lightly
Check that the thread does not take
off upper thread trimmer assembly
Change using parameter No. 63
Adjust the zigzag tension discs by
moving the tension stud bracket in
and out.
Adjust the bar tack tension disc
opening amount to 0.5 -- 1 mm by
removing the top cover and moving
the tension release cam.
Zigzag tension
Increase thread take up to a degree
that needle thread does not take off
upper thread trimmer assembly
Less
LH4-B800E
Cotton yarn #60
Holding force approx. 2 N
(Instruction)
Tack tension
Screw
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4-14
4-15
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4-25
4-26