Janome NH40 Service Manual page 5

Condition
6. Noisy 1. Backlash between hook gear and
operation lower shaft gear is too great.
2. Lower shaft gear is loose.
3. Inappropriate belt tension.
4. Not enough oil
1. Inappropriate feed balance.
7. Deformation
pattern
2. Inappropriate needle swing
timing.
3. Top tension is too strong.
Cause
See mechanical adjustment
"backlash (lower shaft gear)".
Eliminate the looseness.
See part removal and replacement
"driving motor (DC motor)".
Oil all moving parts.
See mechanical adjustment
"stretch stitch feed balance".
See mechanical adjustment
"Needle swing timing".
See mechanical adjustment
"Needle thread tension".
How to fix
3
Reference
P. 14
P. 27
P. 31
P. 18
P. 16
P. 17