JUKI MF-7900 Series Engineer's Manual page 201

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
5-13) Bulge
5-14) Defective chain-off thread
(with top covering stitch)
Cause (1)
From the previous page
12-C) Thread guide
12-D) Top covering thread
take-up
12-E) Needle thread tension
12-F) Threading
12-G) Top covering thread ten-
sion
12-H) Looper thread cam
thread guide position
12-I) Stitch tongue of presser
foot
13-A) Throat plate
13-B) Threading
13-C) Needle thread tension
13-D) Looper thread tension
13-E) Looper thread cam
thread guide position
14-A) Throat plate
14-B) Spreader adjustment
14-C) Looper adjustment
To the next page
Cause (2)
C-1) Flaw, burr in slot
D-1) Drawing-in amount of top covering
thread is too much or too little.
E-1) Needle thread tension is too weak.
F-1) Incorrect threading
G-1) 1st thread tension is too weak.
H-1) Drawing-in amount of looper thread is
too much.
I-1) Thread threading is not smooth due to
incorrect shape of stitch tongue.
A-1) Stitch tongue is too short.
B-1) Incorrect threading
C-1) Tension is too weak.
D-1) Tension is too strong.
E-1) Drawing-in amount of upper thread is
too little.
A-1) Thread threading is not smooth due to
incorrect polishing in stitch tongue.
B-1) Stitch skip in top covering stitch due to
incorrect adjustment.
C-1) Stitch skip due to incorrect adjustment
Check and corrective measures
Replace when modified or its shape is
changed too much.
Refer to the standard adjustment figures.
Increase tension.
Refer to threading diagram.
Increase tension.
Reduce drawing-in amount of thread.
Replace when modified or its shape is
changed too much.
Use throat plate provided with long stitch
tongue.
Refer to threading diagram.
Increase tension.
Reduce tension.
Increase drawing-in amount.
Replace when polished or its shape
changed too much.
Refer to the standard adjustment figures.
Refer to the standard adjustment figures.