JUKI LBH-1790AN, Instruction Manual

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IX. TROUBLES AND CORRECTIVE MEASURES
Troubles Causes Corrective measures Page
1. Needle thread break-
age
1. Thread tension at parallel section is too
high.
2. Pressure or stroke of thread take-up spring
is too large.
3. There is a burr or scratch on the blade
point of hook.
4. Hook timing is not proper.
5. There is a scratch on the thread path.
6. Attaching needle is wrong.
7. Needle is too thin.
8. Needle tip is damaged.
9. Thread breaks when it is bent.
○ Decrease the thread tension at parallel
section.
○ Decrease the tension of thread take-up
spring or decrease its stroke.
○ Buff the blade point of hook. Or, replace
the hook.
○ Adjust again the hook timing with timing
gauge.
○ Polish the thread path with sand paper
and buff it.
○ Adjust again the direction, height, etc.
○ Replace the needle with a thicker one.
○ Replace the needle.
○ Do not pass the thread through the
thread guide pin.
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2. Needle thread slips
off.
1. Needle thread trimmer opens too early.
2. Whip stitching is not formed at the start of
sewing.(Tension at the start of sewing is
too high.)
3. Threading needle thread is wrong.
4. Speed at the start of sewing is too fast.
○ Delay the opening timing of the needle
thread trimmer.
○ Decrease tension at the start of sewing.
○ Thread properly again.
○ Set the soft-start function.
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3. Wobbling at parallel
section
1. Thread tension at parallel section is too
low.
2. Bobbin thread tension is too high.
3. Pre-tension is too low.
○ Increase the thread tension at parallel
section.
○ Decresase bobbin thread tension.
(Purl stitching : 0.05 to 0.1N )
○ Increase pre-tension.
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4. Wobbling at the start
of sewing
1. Thread tension at parallel section is too
low.
2. Position of needle thread trimmer is too
high.
3. Stroke of thread take-up spring is too large.
○ Increase the thread tension at parallel
section.
○ Lower the needle thread trimmer to
such an extent that it does not come in
contact with the presser.
○ Decrease the stroke of thread take-up
spring.
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5. Needle thread ap-
pears on the wrong
side of material at
bar-tacking section in
dumpling condition.
1. Bar-tacking thread tension is too low.
2. Bobbin thread tension is too high.
3. Number of stitches of radial shape is too
many.
4. Tension at the end of sewing is too low.
○ Increase the bar-tacking thread tension.
○ Decresase the bobbin thread tension.
(0.05 to 0.1N )
○ Decrease the number of stitches.
○ Increase tension at the end of sewing.
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6. Stitches float. 1. Bobbin thread tension is too low.
2. Bobbin thread comes off bobbin case. ○ Increase the bobbin thread tension.
○ Perform proper threading the bobbin
case.
○ Take care that the winding amount of
bobbin thread is not excessive.
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7. Stitch skipping 1. Button hole is small in terms of the size of
presser.
2. Material flops because of light-weight.
3. Attaching needle is wrong.
4. Needle is bent.
5. There is a burr or scratch on the blade
point of hook.
○ Replace the presser with a smaller one.
○ Delay the hook-to-needle timing.
(Lower the needle bar by 0.5 mm.)
○ Adjust again the direction, height, etc.
○ Replace the needle.
○ Buff the blade top of hook. Or, replace
the hook.
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