JUKI LK-1900AN Engineer's Manual page 114

Trouble
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6. Defective thread trimming
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Cause (1)
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 ten-
sion is too low.
6-1) Sharpness of the knife is
defective.
6-2) Double cutting for the
needle thread. (Thread
waste remains inside the
cylinder arm cap.)
Cause (2)
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 spread-
ing section A of the moving
knife. The shape of the thread
trimmed becomes and
thread waste remains.
2-B) Shuttle upper spring has scratch-
es. (The shape of the thread
trimmed becomes and
thread waste remains.)
Check and corrective measures
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 height 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.