Needle Thread Mis-Winding - Brother LH4-B800E Service Manual

5. Troubleshooting guide

5-14. Needle thread mis-winding

Cause
Upper thread Scissors installation
scissors height
Scissors gradual
opening timing
Upper thread scissors
opening timing
Upper thread trimmer
movement
Lateral position of
upper thread scissors
Stitch quality Needle thread tension
Zigzag width in the
zigzag stitch portion
Upper Uneven material
clamping foot feeding
Underlay Underlay sewing
5 - 14
Check
Refer to "5-3. Uneven seams 1)"
Adjust the gradual
opening timing to an
appropriate setting.
Adjust the opening
timing to an
appropriate setting.
Polish blade of upper
thread middle trimmer
and upper thread guide
with buffer
Check for burrs on the
top surface of upper
thread middle trimmer
Change the parts
Adjust the lateral
position of the upper
thread scissors.
Decrease tension to
such a degree that it
does not influence
stitch quality
Widen zigzag width to
such a degree that it
does not influence
stitch quality
Increase presser foot
pressure
(Press material so that
the material is properly
stretched)
Reduce the setting for
the sewing start pitch
for underlay sewing
(parameter No. 52) to
around 0.5.
Reduce the underlay
sewing speed
(parameter No. 48).
Solution
Refer to "4-13-7. Adjusting the upper thread
scissors gradual opening timing"
Refer to "4-13-8. Adjusting the upper thread
scissors opening timing"
In case of dull upper thread trimmer
Refer to "5-9. Unraveling of thread
trimmed by upper thread trimmer
assembly"
Refer to "5-11. Needle strikes upper
thread trimmer"
Approx. 1 mm
When using knitted or woven
material, change upper clamping
foot for subclass -3 parts
Parts to change
Length feed plate (subclass -3)
Upper clamping foot assembly (for
knits)
Needle plate 1.2 (subclass -3)
LH4-B800E
page
-
4-14
-
(Instruction)
-
(Instruction)
4-8
-
(Instruction)