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VII. TROUBLES AND CORRECTIVE MEASURES
Trouble
① When the thread gets entangled in the thread take-
Thread
breakage
up lever.
② When the needle thread is threaded in a wrong way. Thread it correctly.
③ When the thread gets entangled in the sewing hook. Remove the entanglement.
④ When the needle thread is excessively tight or loose. Adjust the thread tension.
⑤ When the needle thread slips in the rotary tension.
⑥ When the tension of the thread take-up spring is
excessively high or low.
⑦ When the stroke of the thread take-up spring is ex-
cessively large or small.
⑧ When the timing of the sewing hook and the needle
is not matched.
⑨ When there is a scratch on the thread path of hook,
bobbin case, thread take-up lever or any other part.
⑩ When the thread is not suitable.
a. The quality of the thread is poor.
b. The thread is too thick for the needle.
c. The thread is broken by heat.
⑪ When the stitch is skipped.
① The thread remaining at the needle tip after thread
At the
beginning
trimming is too short.
of sewing,
a. The thread tension provided by the pretension
several
disk is too high.
stitches
skip or
b. The tension disk does not float at the time of
the thread
thread trimming.
slips out
c. The tension disk comes in contact with the thread
of the
take-up spring guard.
needle
d. The cam timing is too early.
eyelet.
② Thread drawn-out amount is insufficient.
a. Position of the thread draw-out wire is defective.
b. Thread slips out of the thread draw-out wire and/
or the thread guide.
③ The bobbin thread tension is too strong to cause a
thread trimming failure. As a result, the length of bob-
bin thread remaining after thread trimming is too short.
④ Defective clamping of the bobbin thread due to dete-
rioration of the clamp felt.
⑤ The sewing speed at the beginning of sewing is
too high. As a result, the needle thread and bobbin
thread are not smoothly intertwined.
⑥ Threads are rubbed by the counter knife and broken
before the moving knife and the counter knife en-
gage with each other. The length of thread remaining
at the needle tip after thread trimming varies.
⑦ Blind stitches are sewn at the beginning of sewing.
The needle thread and the bobbin thread fail to make
knots since no fabric resistance is applied to them.
Cause
– 58 –
Corrective measures
Remove the entanglement.
Increase the tension of the pretension
disk.
Adjust the tension of the take-up spring.
Adjust the stroke of the take-up spring. (8
to 12 mm)
Adjust the timing.
Remove such a scratch or replace the
component.
Use a thread of good quality.
Use a suitable thread or needle.
Use JUKI Silicone Oil Lubricant unit.
Refer to the following paragraphs, Stitch
skipping.
Loosen the pretension disk to such an
extent that the thread and the rotary disk
do not slip.
Inspect and adjust the tension release
solenoid components.
Adjust their positions to prevent them
from coming in contact with each other.
Adjust the timing of thread trimming.
Adjust the position of the thread draw-
out wire.
Re-thread the thread draw-out wire and
thread guide. If the thread frequently
slips out of the thread draw-out wire,
change the wire with a new one.
Loosen the bobbin thread tension to
such an extent that a sufficient thread
tension is provided.
Change the clamp felt with a new one.
Adjust the soft-start speed to 800 sti/
P07
min. Item No.
Adjust the number of stitches to be sewn
with the soft-start function to "4". Item
P08
No.
Re-sharpen the counter knife, or change
it with a new one.
Place the threads under the presser
foot at the beginning of sewing and start
sewing while retaining them by hand.
See
page
14
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21
16
16
16
16
21
16
23
23
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