34
4
Cause of troubles and troubleshooting
1) Sewing machine troubleshooting
No
Symptom
Checkpoints
Root cause
Corrective action
1
2
Needle breaks
Direction and height of
needle
Needle
Feed dog timing
Gap between needle and
hook
Threading method
Needle
Direction and height of
needle
Upper thread tension
Lower thread tension
Thread take up stroke
Hook
Feed dog
Needle plate
Thread tension
Thread take up spring
tension
Gap between opener and
hook
Direction and height of
needle
Needle
Threading
Hook timing
Gap between the needle
and the hook
Remaining upper thread
length after trimming
Lower thread holder
Check the up-stop
position of the needle
Check the oil felt tension
of upper thread
Needle is inserted into wrong position
Needle is bent
Bad timing of feed dog
Bad timing of needle and hook
Adjust the timing of needle and hook
Wrong threading (inserted from the
opposite side)
Bent needle
Needle inserted in the wrong direction
and height
Too tight upper thread tension
Too loose lower thread tension
Too large stroke
There is a scratch on the hook edge
There is a scratch on the needle hole of
the feed dog
There is a scratch on the thread case
and around the needle plate
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
Needle and hook are too far apart
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 upper thread oil felt is pressing the
thread too strongly.
Reinsert the needle correctly and push in
to its highest level.
Change the needle
Adjust the timing of feed dog
The heads of the needle and the hook
interfere each other.
Adjust the location of the hook
Thread the needle correctly
Change the needle
Insert the needle correctly
Reduce the tension of upper thread
Reduce the tension of lower thread
Adjust the stroke level
Remove the scratch on the hook edge
Remove the scratch on the feed dog
Remove the scratch on the needle plate.
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
Adjust the position of the 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
Adjust the felt tension
Thread breaks
3
Poor thread
adjustment
Upper thread
falls out when
starting to sew or
sewing is
skipped.
4
