JUKI LK-1900A Series Engineer's Manual page 103

Trouble
5. Thread breakage at the time of
thread trimming.
6. Defective thread trimming
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Cause (1)
5-1) Thread release timing is
defective.
5-2) Thread spreading section of the
moving knife has scratches.
5-3) Shuttle upper spring has
scratches.
5-4) Level difference between the
needle hole guide and the
counter knife is too high.
5-5) Clearance between the needle
hole guide and the counter
knife is too small.
5-6) Lower face of the needle hole
guide has scratches.
5-7) Thread spreading timing of
the moving knife is defective.
5-8) Thread take-up spring tension
is too low.
6-1) Sharpness of the knife is
difective
6-2) Double cutting for the needle
thread. (Thread waste remains
inside the cylinder arm cap.)
Cause (2)
1-A) Floating amount of the thread
tension disk No. 2 is small.
4-A) Thread is cut before trimming
with the blade section of the
moving knife.
5-A) Thread is cut before trimming
with the blade section of the
moving knife.
6-A) Thread is cut with the needle
hole guide.
1-A) Worn-out of the moving and
counter knives.
1-B) Engagement of the moving
and counter knives is defective.
1-C) Parallel of the blade section
of counter knife is defective.
1-D) Attaching position of the
counter knife is defective.
2-A) There is a burr on thread spreading
section of the moving knife.
A
The shape of the thread
trimmed becomes and
thread waste remains.
A
2-B) Shuttle upper spring has scratches.
(The shape of the thread trimmed
becomes and thread waste
remains.)
Check and corrective measures
Adjust the amount of thread tension No. 2 floating.
Paying attention to the blade section, polish with
polishing powder.
Remove the scratches.
Properly adjust the position of counter knife.
Properly adjust the position of counter knife.
Remove the scratches and polish with buff, or replace
the needle hole guide.
Adjust initial positions of the presser origin sensor,
thread trimmer, and the moving knife.
Adjust the thread take-up spring.
Replace the moving and counter knives.
Properly adjust the heigh and position of the moving
and counter knives.
Properly adjust the parallel of the blade section of
counter knife.
Properly adjust the attaching position of counter knife.
Paying attention to the blade section, polish with
polishing power, or replace the moving knife.
Remove the scratches.