Brother NV4000D Service Manual page 344

Failure Investigation for Electronic Parts Thread tensioning does not go well
Is the thread tension adjuster gap correct?
5 - 18
From previous page
Is the resistance between pins 1 & 1, 2
& 2, 3 & 4, and 4 & 3 at the ends of the
AT pulse motor lead wire 1 Ω or less?
Y
Is the resistance between pins 1 & 2
and 3 & 4 on the AT pulse motor
connector (CN8) between 5 and 7 Ω?
Y
Is the inner rotary hook tension right?
Y
Y
Replace main PCB assy.
N
Replace the AT pulse motor
lead wire.
N
Replace the pulse motor.
N
Adjust inner rotary hook tension
N
Adjust upper thread tension disk