JUKI DDL-9000C-S Series Engineer's Manual page 186

Trouble
4. Stitch skipping
The machine fails to form a com-
plete stitch.
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Cause (1)
4-1) The needle is defective.
4-2) The matters related to the
hook are inappropriate.
4-3) The tension of the needle
thread is too high.
4-4) The sewing speed is too high.
4-5) The feed timing is inappropri-
ate. (Needle bent)
Cause (2)
1-A) The needle is bent.
1-B) The needle mounting direction
is inappropriate. The needle is
not mounted fully to the end.
1-C) The needle tip is blunt.
1-D) The needle is too thin or thick
for the thread to be used.
2-A) The blade top of the hook is
blunt or worn.
2-B) The timing of the hook is inap-
propriate.
2-C) The height of the needle bar is
inappropriate.
2-D) The clearance between the
hook point and needle is wrong.
2-E) The loop shape is unstable.
(Mesh type materials)
2-F) A needle holder does not exist.
5-A) The needle is bent by the thick
portion.
Check and corrective measures
Replace the needle.
Mount the needle appropriately. Replace the
needle clamp screw.
Defective sewing is likely to occur when the
needle recess portion faces frontward.
Replace the needle.
Replace the needle.
Sharpen the blade top of the hook or replace
the hook.
Correct the timing. (The proper timing depends
on the type of material and thread. In general,
the timing should be set earlier for synthetic
thread or heavy-weight material, and it should
be set later for light-weight material.)
Properly adjust it with respect to the hook
point.
Minimize the clearance.
Wind the needle thread or use the T-type
thread guide.(B1418227T00).
Replace the current hook with a hook with a
needle holder equipped. 11141355 for MS,
22890404 for SH
Reduce the tension of the needle thread. Use
silicon.
Reduce the sewing speed.
Hasten the feed timing.