JUKI MF-7900 Series Engineer's Manual page 191

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
5-2) Looper does not scoop
the middle needle thread.
To the next page
Cause (1)
2-A) Looper A-1) Incorrect shape of pointed end of loop-
2-B) Needle B-1) Needle bend, incorrect needle mount-
2-C) Auxiliary thread tension C-1) Being used.
2-D) Needle thread guide rod D-1) Height is too low.
2-E) Needle height E-1) Needle bar height is too low.
2-F) Threading F-1) Incorrect threading
2-G) Needle thread guard G-1) Being used.
2-H) Spreader H-1) Spreader thread tension is too strong.
2-I) Needle heat I-1) Stitch skip occurs before thread break-
2-J) Looper adjustment J-1) Incorrect clearance adjustment, incor-
2-K) Needle guard, front and K-1) Incorrect contact amount, incorrect
rear
Cause (2)
er disables scooping a loop.
ing direction, wrong needle
age produced by needle heat.
rect returning amount adjustment
height
Check and corrective measures
Replace it with the genuine part.
Replace the needle with new one. Cor-
rect the mounting direction.
Use UY128GAS.
Do not use.
Correct the height to appropriate height.
Refer to the standard adjustment figures.
Refer to threading diagram.
Do not use.
Reduce the tension.
Same described in page "Thread break-
age by needle heat"
Refer to standard adjustment.
Refer to the standard adjustment figures.