JUKI MF-7900 Series Engineer's Manual page 199

WARNING :
Turn OFF the power before starting the work so as to prevent accidents caused by abrupt start of the sewing machine
Trouble (1) Trouble (2)
From the previous page
5-9) Double bonding stitch
(Middle, Left)
5-10) Irregular stitches
(Left, Middle, Right)
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Cause (1)
9-A) Throat plate
9-B) Needle
9-C) Looper
9-D) Needle height
9-E) Threading
9-F) Needle thread tension
9-G) Needle thread guide rod
9-H) Auxiliary thread tension
10-A) Throat plate
10-B) Spreader adjustment
10-C) Looper
10-D) Top covering thread
take-up
10-E) Needle thread tension
To the next page
Cause (2)
A-1) R of stitch tongue in throat plate is too
large. Stitch tongue is too short.
B-1) Worn out needle point, needle bend,
wrong needle
C-1) Flaw in looper's ventral section, incor-
rect polishing
D-1) Needle bar position is too low.
E-1) Incorrect threading
F-1) Tension is too weak.
G-1) Substandard lower positioning of
thread guide
H-1) Use nipper is likely to generate this
trouble.
A-1) Incorrect polishing
B-1) Stroke of spreader is too large.
C-1) Worn out looper's pointed end and
incorrect polishing
D-1) Drawing-in amount of top covering
thread is too much.
E-1) Needle thread tension is too weak.
Check and corrective measures
Replace it with the genuine part.
Replace needle with new one.
Use UY128GAS.
Replace the looper when modified or its
shape is changed too much.
Refer to the standard adjustment figures.
Refer to threading diagram.
Increase tension.
Adjust the thread guide position upward.
Do not use nipper.
Polish correctly.
Refer to the standard adjustment figures.
Replace the looper when modified or its
is shape changed too much.
Refer to the standard adjustment figures.
Increase tension.