Brother PE770 Service Manual page 215

Repair Manual
Problem Primary factors and causes
6 Irregular rotation Grease or dust adhering to
(rotation slow / fast speed shutter
/ unstable)
Grease or dust adhering to NP
sensor
Bad NP PCB assy.
Interference between NP PCB
assy. and speed shutter
• Damage to speed shutter
• Damage to NP PCB assy.
Bad motor PCB assy.
Bad main PCB assy.
7 Sewing sounds
Inappropriate
sounds
• Thread take- Shaft noise
up noise
• Loose screws
• Outer rotary Outer rotary hook vertical rattle
hook noise
• Upper shaft Upper shaft bushing out of oil
noise
Rattle along the thread take-up
counter weight shaft
• Motor noise Belt too tight
Motor brush noise
• Lower shaft Lower shaft bushing out of oil
noise
Lower shaft axial rattle
• Needle Noise of contact between needle
contact noise and outer rotary hook
• Bad needle interference
• Loose needle interference
6 - 4
adjustment
adjustment screw
Repair method
Remove grease or dust
Remove grease or dust
Replace NP PCB assy.
(2-17) (3-25)
Eliminate cause of interference
Replace upper shaft assy.
(2-32) (3-5)
Replace NP PCB assy.
(2-17) (3-25)
Replace motor PCB assy.
(2-15) (3-25)
Replace main PCB assy.
(2-7) (3-34)
Retighten screws
(2-41) (3-43)
Reattach outer rotary hook
(2-46) (3-56)
Lubricate upper shaft bushing
(3-5)
Reattach thread take-up counter
weight (2-42) (3-42)
Adjust motor belt (4-7)
Replace main motor assy.
(2-15) (3-25)
Lubricate lower shaft bushing
(3-53)
Reattach lower shaft B assy.
(2-47) (3-55)
Adjust needle interference
Items for Inspection method
Inspection and standards
Machine Rotate smoothly.
operation while
rotating
Operating noise Check that there is no
abnormal noise at
sewing.