SunStar KM-250 Series User Manual page 30

No Symptom
Upper thread
4
does not sink.
Lower thread
5
does not sink.
Tension of fixed blade
Edge of movable and fixed blades
6 Trimming errors Direction of needle
Check the crossing of
trimmer cam notch
mark and blade
Upper thread
is pulled out
7
when sewing
Check the Up-stop
commences.
position of needle
30
Checkpoints
Too tight upper thread tension.
Too loose lower thread tension.
Too weak upper thread tension.
Increase tension of upper thread.
Tension not aligned between movable and fixed blade.
Abrasion in blade groove of movable and fixed blade.
Wrong needle insertion.
Insufficient crossing quantity of
movable and fixed blade.
Too strong upper thread tension.
Too thick a needle for thread.
Take-up lever pulls out the upper
thread because the needle up and
down position is too high.
Keystone Sewing Machine Company, Inc.
Root cause
Reduce tension of upper thread.
Increase tension of lower thread.
Too strong lower thread tension.
Decrease tension of lower thread.
Adjust tension of movable and fixed blade.
Replace movable and fixed blade.
Reinsert the needle correctly.
Adjust the stroke of movable and
fixed blade.
Adjust tension of upper thread.
Check thickness of needle.
Adjust the up-stop position of
needle.
Corrective action