Troubles And Corrective Measures - JUKI LBH-1790S Instruction Manual

IX. TROUBLES AND CORRECTIVE MEASURES
Troubles
1. Needle thread break- 1. Thread tension at parallel section is too
age
2. Pressure or stroke of thread take-up spring
3. There is a burr or scratch on the blade
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.
2. Needle thread slips 1. Needle thread trimmer opens too early.
off.
2. Whip stitching is not formed at the start of
3. Threading needle thread is wrong.
4. Speed at the start of sewing is too fast.
3. Wobbling at parallel 1. Thread tension at parallel section is too
section
2. Bobbin thread tension is too high.
3. Pre-tension is too low.
4. Wobbling at the start 1. Thread tension at parallel section is too
of sewing
2. Position of needle thread trimmer is too
3. Stroke of thread take-up spring is too large.
5. Needle thread ap- 1. Bar-tacking thread tension is too low.
pears on the wrong 2. Bobbin thread tension is too high.
side of material at
bar-tacking section in 3. Number of stitches of radial shape is too
dumpling condition.
4. Tension at the end of sewing is too low.
6. Stitches float. 1. Bobbin thread tension is too low.
2. Bobbin thread comes off bobbin case.
7. Stitch skipping 1. Button hole is small in terms of the size of
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
Causes
high.
is too large.
point of hook.
sewing.(Tension at the start of sewing is
too high.)
low.
low.
high.
many.
presser.
point of hook.
Corrective measures
○ 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.
○ Delay the opening timing of the needle
thread trimmer. (Refer to Engineer's
Manual for "Needle thread trimming
adjustment mode".)
○ Decrease tension at the start of sewing.
○ Thread properly again.
○ Set the soft-start function.
○ Increase the thread tension at parallel
section.
○ Decrease bobbin thread tension.
(Purl stitching : 0.05 to 0.1N )
○ Increase pre-tension.
○ 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.
○ Increase the bar-tacking thread tension.
○ Decrease the bobbin thread tension.
(0.05 to 0.1N )
○ Decrease the number of stitches.
○ Increase tension at the end of sewing.
○ Increase the bobbin thread tension.
○ Perform proper threading the bobbin
case.
○ Take care that the winding amount of
bobbin thread is not excessive.
○ 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.
– 85 –
Page
27
75
–
72
–
16
16
16
13
73
41
17
56
27
18
–
27
73
75
27
18
39
56
18
17
29
–
72
16
16
–