JUKI MF-7900 Series Engineer's Manual page 200

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
5-11) Ill-tensed seam
5-12) Irregular stitches in top
covering stitches
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Cause (1)
From the previous page
10-F) Threading
10-G) Top covering thread ten-
sion
10-H) Looper thread cam
thread guide position
11-A) Throat plate
11-B) Needle
11-C) Looper
11-D) Needle height
11-E) Threading
11-F) Needle thread tension
11-G) Needle thread guide rod
11-H) Looper thread tension
11-I) Looper thread cam
thread guide position
12-A) Spreader
12-B) Spreader adjustment
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Cause (2)
F-1) Incorrect threading
G-1) Thread tension is too weak.
H-1) Drawing-in amount of looper thread is
too much.
A-1) Incorrect polishing. Too long stitch
tongue.
B-1) Worn out needle point, needle bend,
wrong needle
C-1) Worn out looper's pointed end, incor-
rect polishing
D-1) Needle bar position is too low.
E-1) Incorrect threading
F-1) Tension is too weak.
G-1) Either the position of thread guide is
too low or too high.
H-1) Tension is too strong.
I-1) Drawing-in amount of looper thread is
too little.
A-1) Flaw in pointed end of spreader ob-
structs smooth thread threading.
B-1) Spreader stroke is too large.
Check and corrective measures
Refer to threading diagram.
Increase tension.
Reduce drawing-in amount of thread.
Correct or replace part.
Replace needle with new one.
Use UY128GAS.
Replace the looper when modified or its
is shape changed too much.
Refer to the standard adjustment figures.
Refer to threading diagram.
Increase tension.
Refer to the standard adjustment figures.
Reduce tension.
Increase drawing-in amount of thread.
Replace when modified or its shape is
changed too much.
Refer to the standard adjustment figures.