JUKI MF-7900 Series Engineer's Manual page 193

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
5-4) Needle does not scoop
the looper thread. (Tri-
angle stitch skip) Middle
needle • Left needle
To the next page
Cause (1)
4-A) Looper A-1) Ventral shape is incorrect.
4-B) Needle B-1) Needle bend
4-C) Needle height C-1) Needle bar position is too high.
4-D) Threading D-1) Incorrect threading
4-E) Looper adjustment E-1) Incorrect clearance adjustment, incor-
4-F) Looper thread tension F-1) Tension is too weak.
4-G) Looper thread cam tim- G-1) Looper thread cam timing is too early.
ing
Cause (2)
rect returning amount
Check and corrective measures
Replace it with the genuine part.
Replace the needle with the new one.
Refer to the standard adjustment figures.
Refer to threading diagram.
Refer to the standard adjustment figures.
Increase tension.
Refer to the standard adjustment figures.