JUKI MF-7800D Series, Engineer'S Manual

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2-4) Thread 4-A) Poor quality and weakness of thread Replace it with good quality of thread.
2-5) Looper avoid 5-A) Too strong contact of looper back with Adjust longitudinal momentum of the looper and
needle resulting in thread breakage make the looper contact the needle at 1/3 height from
the bottom surface of the back of looper.
2-6) Needle heat 6-A) In case needle heat is generated looper Refer to needle heat in needle breakage
thread’s contact with needle causes
thread breakage, specially at the time
machine is at rest.
3. Needle breakage 3-1) Needle entry 1-A) Needle hits the throat plate or presser foot Align the needle entry to the needle.
because the needle entry is not correctly
positioned for the plate or foot.
3-2) Spreader 2-A) Too little clearance between spreader Refer to the standard adjustment figures.
and needle
3-3) Interference of looper with scooping 3-A) Needle hits looper resulting in needle Make adjustment so that looper does not hit the
movement of needle breakage. looper. For the correction of the contact at looper’s
back, adjust the moving amount, front and rear.
3-4) Needle guard 4-A) Too strong contact against needle guard Refer to the standard adjustment figures.
or needle point hits needle guard due to
incorrect position.
3-5) Needle thickness No. 5-A) Too thin needle for fabric used Use thicker needle.
3-6) Thread tension 6-A) Needle thread tension is too strong. Reduce the needle thread tension.
3-7) Feed height, Needle height 7-A) Feed dog is too high or needle height is Refer to the standard adjustment figures.
too low resulting in needle breakage due
to needle swerve.
4. Worn out needle point 4-1) Needle guard 1-A) Incorrect height or incorrect position, Check to see the height of needle guard and
front and rear clearance between needle guard and needle.
4-2) Interference with looper 2-A) Moving amount, front and rear is ill Adjust moving amount, front and rear and correct
balanced. the incorrect position of looper’s back and the
contact when it returns.
Trouble Cause (1) Cause (2) Corrective measures
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