3
MODEL 520
CONDITION
CAUSE
HOW TO FIX
REFERENCE
6. Noisy
operation
1. Backlash between shuttle hook
gear and lower shaft gear is too
great.
2. Lower shaft gear is loose.
3. Inappropriate belt tension.
4. Not enough oil.
See mechanical adjustment
“Backlash (lower shaft gear)”.
Eliminate the looseness.
See part removal and replacement
“driving motor (DC motor)”.
Oil all moving parts.
P. 14
P. 28
P. 36
7. Deformation
pattern
1. Inappropriate feed balance.
2. Inappropriate zigzag
synchronization.
3. Upper thread tension is too
strong.
See mechanical adjustment
“Stretch stitch feed balance”.
See mechanical adjustment
“Zigzag synchronization”.
See mechanical adjustment
“Needle thread tension”.
p. 18
P. 16
P. 17
