JUKI LU-1520NCS-7, Instruction Manual

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33. TROUBLES IN SEWING AND CORRECTIVE MEASURES
Troubles Causes Corrective measures
1. Thread breakage
(Thread frays or is worn
out.)
(Needle thread trails 2 to 3
cm from the wrong side of
the fabric.)
①
Thread path, needle point, hook blade
point or bobbin case resting groove
on the throat plate has sharp edges or
burrs.
②
Needle thread tension is too high.
③ Bobbin case opening lever provides
an excessive clearance at the bobbin
case.
④ Needle comes in contact with the
blade point of hook.
⑤
Amount of oil in the hook is too small.
⑥
Needle thread tension is too low.
⑦
Thread take-up spring works exces-
sively or the stroke of the spring is too
small.
⑧
Timing between the needle and the
hook is excessively advanced or re-
tarded.
◦ Remove the sharp edges or burrs on the
blade point of hook using a fine emery pa -
per. Buff up the bobbin case resting groove
on the throat plate.
◦ Decrease the needle thread tension.
◦ Decrease the clearance provided between
the bobbin case opening lever and the bob-
bin.
Refer to "21. ADJUSTING THE BOBBIN
CASE OPENING LEVER" p. 17 .
◦ Refer to "19. NEEDLE-TO-HOOK RELA-
TION" p. 16
.
◦ Adjust the amount of oil in the hook proper -
ly.
Refer to "7. LUBRICATION" p. 8 .
◦ Increase the needle thread tension.
◦ Decrease the tension of the spring and
increase the stroke of the spring.
◦ Refer to
"19. NEEDLE-TO-HOOK RELA-
TION" p. 16 .
2. Stitch skipping ① Timing between the needle and the
hook is excessively advanced or re-
tarded.
②
Pressure of the presser foot is too low.
③ The clearance provided between the
top end of the needle eyelet and the
blade point of hook is not correct.
④
Hook needle guard is not functional.
⑤ Improper type of needle is used.
◦ Refer to "19. NEEDLE-TO-HOOK RELA-
TION" p. 16 .
◦ Tighten the presser spring regulator.
◦ Refer to
"19. NEEDLE-TO-HOOK RELA-
TION" p. 16 .
◦ Refer to "20. ADJUSTING THE HOOK
NEEDLE GUARD" p. 17 .
◦ Replace the needle with one which is thick -
er than the current needle by one count.
3. Stitch skipping at the start
of sewing
①
Bobbin thread is not clamped after
thread trimming.
② Sewing speed is too fast and needle
thread cannot catch bobbin thread.
③ Bobbin thread tension is too low.
④ During the previous sewing, thread
trimming was carried out at a position
which is located outside the material
edge.
◦ Check again the installing position of clamp
spring and clamping pressure.
◦ Increase the number of stitches of soft
start at the setting of motor. (Refer to the
Instruction Manual for the SC-922 for how
to change the setting.)
◦ Increase the bobbin thread tension.
◦ Carry out thread trimming on the material.
◦ Change the function setting No. 158 to "1"
to change the thread trimming method to
the 1-stitch condensation thread trimming
(*1). (Refer to the Instruction Manual for the
SC-922 for how to change the setting.)
*1 "1-stitch condensation thread trimming" means the thread trimming operation during which a condensation stitch is
sewn before carrying out thread trimming.