Thread Tensioning Is Not Correct - Brother PE770 Service Manual

Failure Investigation for Electronic Parts Thread tensioning is not correct
Is the bobbin thread installed correctly?
Is the combination of fabric, thread
and needle correct?
It the resistance between the 1 & 2
pins, and 3 & 4 pins on the AT pulse
motor connector (CN9) 4 – 9 Ω ?
Is the inner rotary hook (lower
thread) tension correct?
Does the tension disk move correctly?
5 - 12

Thread tensioning is not correct.

Is the upper thread threaded correctly?
Y
Y
Y
Y
Y
Y
Replace the main PCB assy.,
or
Replace the motor PCB assy.,
or
Replace the FFC.
N
Correct the upper threading.
N
Install the bobbin thread correctly.
N
Use the correct combination.
N
Adjust the upper thread tension.
N
Adjust the inner rotary hook
tension.
N
Reassemble the thread tension
unit.