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4. TROUBLES AND CORRECTIVE MEASURES (MECHANICAL PARTS)
Troubles
Cause (1)
Cause (2)
Checking orders and corrective measures
1.
Stitch skipping of 1 to 2 stitches occurs at
the sewing start.
Needle thread remaining at the top of
needle after thread trimming is too short.
Needle thread path is defective, and needle
thread tension when trimming thread is too
high.
Tension of thread tension disk No. 1 is too
high.
Rising amount of thread tension disk No. 2
when trimming thread is incomplete.
Thread trimmer cam timing is too early.
Position of thread take-up picker is
improper, and needle thread slips off when
trimmming thread.
Counter knife is excessively near to needle.
Blade point is too sharp.
There are scratches on knife thread guide,
moving knife or hook.
Lifting amount of auto lifter (AK118) is too
large.
Check needle thread routing, thread entangled on thread guide
rod or the direction, and position of thread stand or thread
entangled on it.
Turn thread tension nut of thread tension disk No. 1 to the left to
decrease tension.
Check that rising amount of thread tension disk No. 2 is 0.5 to 1
mm when thread take-up picker is pressed until the top end comes
in contact with bobbin.
Adjust the rising amount with the position of thread tension release
wire (3-8) in the rear side on machine bed. Check that the disk is
loosened paralell. If not, turn thread tension spring by 180˚ or
correct the tilt of the spring.
Check and adjust thread trimmer cam timing referring to (3-5).
Change the red dot to green dot adjustment.
Press plunger with finger so that thread trimmer solenoid is in
sucked state, and when thread take-up picker is pressed until
the top end comes in contact with bobbin and there is a clearance
at the top end of thread take-up picker, readjust the thread take-
up picker referring to (3-12).
Remove throat plate, and check position of counter knife or
scratch on moving knife to adjust them. (3-7)
Check scratches on hook (especially hook blade point) and hole
of knife thread guide. If there are scratches on them, polish enough
with buff. Replace the part if scratch is large.
Lift of the auto-lifter is too high, presser bar thread guide lifts
quickly and needle thread is pulled with the thread take-up spring.
As a result, needle thread becomes short.
Readjust the lift of AK device to approximately 9 mm. When using
AK device, make the remaining amount of needle thread slightly
longer.
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