Brother PE770 Service Manual page 216

Repair Manual
Problem Primary factors and causes
8 Threading not Thread pushed out at the hook
possible end
• Vertical slippage in needle
thread block
Hook extends right of the needle
hole
• Wide gap between right side
of needle and hook guide
• Needle curvature
• Needle slant (hole slant with
slanted attachment of
needle block)
• Threader hook assy.
slippage
Does not go into needle hole
because of hook tip curvature
When the threader Threader shaft tangling
lever returns, it
stops part way
Bad thread guide shape
through.
Needle thread shaft and top gap
too small
Needle thread Bad needle stop position
lever operation
• Bad NP PCB assy.
catches part way
through.
• Grease or dust adhering to
NP PCB assy.
• Rotation shutter damage
• Bad needle thread block
rotational position
9 Either upper thread Upper thread tension is tight/
tension or lower loose
thread tension
Lower thread tension is too tight/
loose
Upper thread or lower thread
unsuitable
Repair method
Adjust needle thread (4-14)
Replace threader hook assy.
(2-40) (3-45)
Replace needle
Replace needle bar
(2-37) (3-49)
Replace threader hook assy.
(2-40) (3-45)
Replace threader hook assy.
(2-40) (3-45)
Replace needle bar supporter
assy. (2-38) (3-47)
Replace hook assy.
(2-40) (3-45)
Replace needle bar supporter
assy. (2-38) (3-47)
Replace NP PCB assy.
(2-17) (3-25)
Remove grease or dust
Replace upper shaft assy.
(2-32) (3-5)
Adjust needle thread block
Adjust upper thread tention
(4-9)
Adjust lower thread tension
(4-19)
Replace upper thread or lower
thread
Items for Inspection method
Inspection and standards
Threading Con firm that the
function threading lever moves
smoothly and that
threading through the
needle hole is possible.
Upper thread Check that the thread
tension tension is good during
actual sewing.
Lower thread
tension
6 - 5