JUKI LU-2800 Series, Engineer'S Manual

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WARNING :
Turn OFF the power before starting the work so as to prevent accidents caused by abrupt start of the sewing machine.
Trouble Cause Checking Corrective measures
5. Loose stitches (Balloon stitches
or isolated idling loop)
5-1) Clearance between the opener and
the protruding section of inner hook is
too large.
1-A) Check the clearance. Refer to “2.-(5) Adjusting the opener”.
5-2) Thread paths have been poorly fin -
ished.
2-A) Check the finish of the respec -
tive thread paths.
Finish using a fine emery paper or buff.
5-3) Bobbin fails to move smoothly. 3-A) Check the change of bobbin
thread tension.
Replace the bobbin or the hook with new ones.
5-4) Thread is not well tightened in the
reverse feed.
4-A) Walking foot is not of top-divid-
ed type.
Use the optional walking foot and presser foot.
5-5) Height of the feed dog is too high. 5-A) Compare the height with the
standard value.
Refer to “2.-(3) Height of the feed dog”.
Lower the height by 0.2 mm than the standard
value.
5-6) Feed timing is excessively advanced. Retard the feed timing.
5-7) Hard-to-slip thread is used. Use silicon oil. (Refer to * below.)
* Use separately available parts below :
• 21144308 Needle thread lubricator
• B1114012000 Thread guide rod
• B91351230B0 Silicon oiler
5-8) Bobbin thread does not pass through
the tension spring of the inner hook.
Thread the bobbin thread correctly.
5-9) Bobbin thread tension is too low. Increase the bobbin thread tension.
5-10) Bobbin has been wound too tightly. 10-A) Check thread winding condition. Decrease the tension applied to the bobbin winder.
5-11) The needle thread tension is low
while carrying out the reverse feed
stitching.
Advance the horizontal feed timing.