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4
Causes of Troubles and Troubleshooting
1) Sewing machine troubleshooting
No
Symptom
Direction and height of
needle
Needle
Timing of feed dog
Needle breaks
Ascending level of needle
bar
Height of needle
Gap between needle and
hook
Threading method
Needle
Direction and height of
needle
Thread breaks
Upper thread tension
Lower thread tension
Working capacity of take-up
lever spring
Thread tension
Thread take up spring
Poor thread
tension
adjustment
Gap between opener and
hook
Direction and height of
needle
Needle
Threading
Gap between the needle
Upper thread falls
and the hook
out when starting
Remaining upper thread
to sew or sewing is
length after trimming
skipped.
Lower thread holder
Check the up-stop position
of the needle
The gap between the
movable knife and the hook
Check the tension of fixed
knife
Trimming miss
Direction of the needle
Blade side of movable and
fixed knives
Trimming cam timing
Thread release stroke
Trimming timing
Opening of the thread
tension adjusting plate
Too short thread
Tension of auxiliary thread
length after
tension adjustment assembly
trimming
Thread take up stroke
Thread release adjustment
volume on the control box
28
Checkpoints
Needle is inserted into wrong position
Needle is bent
Bad timing of feed dog
Bad timing of needle and hook
Bad timing of needle and hook
Bad timing of needle and hook
Wrong threading
Bent needle or broken needle tip
Needle inserted in the wrong position
Too tight upper thread tension
Too tight lower thread tension
Loose upper thread
Upper and lower thread tensions are bad
Thread take up spring tension is inadequate
The gap between the opener and hook is
inadequate
Needle is inserted into wrong position
Needle is bent
Wrong direction
The timing between the needle and hook is
bad
The length of the remaining upper thread is too
short
After trimming, lower thread holder does not
hold the lower thread
Due to problems in the up-stop position of the
needle, the thread take up lever pulls the upper
thread out of the needle when the sewing starts
The height and distance between the movable
knife and the hook do not match
Tension and contact of movable and fixed
knives are bad
Needle is not inserted correctly
Scratch and abrasion of movable and fixed
knives
The timing of trimming cam is wrong
Thread release stroke is too small
Wrong trimming timing
The opening on the thread tension control plate
is too small
Too strong tension on the auxiliary thread
tension control assembly
Thread take up stroke is too large
Volume is adjusted to too low
Root cause
Reinsert the needle correctly
Change the needle
Adjust the timing of feed dog
Adjust the timing of needle and hook
Adjust the timing of needle and hook
Adjust the timing of needle and hook
Thread the needle correctly
Change the needle
Insert the needle correctly
Reduce tension of upper thread
Reduce tension of lower thread
Adjust take-up lever spring
Adjust the upper and lower thread tensions
Adjust the thread take up spring tension
Adjust the gap between the opener and hook
Reinsert the needle correctly and push in to its
highest level.
Change the needle
Insert the thread in the right way.
Adjust the timing between the needle and hook
Increase the adjustment volume of the upper
thread on the control box
Adjust the location and tension of the lower
thread holder.
Readjust the needle' s up-stop film position
Readjust the movable knife setting position
Correct the tension adjustment and surface
contact of movable and fixed knives.
Insert the needle correctly
Replace movable knife or fixed knife.
Adjust the timing of trimming cam
Readjust the thread release stroke
Adjust the trimming timing
Adjust the thread release stroke
Adjust the tension of the auxiliary thread
tension control assembly
Adjust the thread take up stroke
Increase the volume adjustment.
Corrective action
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