Brother DH4-B981 Instruction Manual page 79

Problem
Upper thread is not cut.
Lower thread is not cut.
Thread slips out of the needle at
the sewing start.
Material is not being cut cleanly.
Cause
Knife is blunt.
Knife does not move to the full stroke
because air pressure is too weak.
Upper thread trimmer knife is not
picking up the upper thread.
Movable knife is not picking up the needle
thread because the last stitch is being skipped.
Movable knife position is incorrect.
Knife is blunt.
Knife does not move to the full stroke
because air pressure is too weak.
Movable knife position is incorrect.
Thread nipper spring force is too
weak.
Upper thread length is too short
after trimming.
Needle and looper adjustment is
incorrect.
Not enough upper thread is being
fed out.
Knife and hammer are not con-
tacting properly.
Cutting pressure is too weak.
Knife is blunt.
DH4-B981
11. TROUBLESHOOTING
Remedy
Replace with a new knife.
Adjust the air pressure.
Install the upper thread trimmer knife so that
it cuts only one side of the upper thread loop.
Refer to the remedies given under "Skipped
stitches occur" in this troubleshooting chart.
Adjust the position of the movable
knife or the loop spreader.
Replace with a new knife.
Adjust the air pressure.
Adjust the position of the movable
knife or the loop spreader.
Adjust the force of the thread
nipper spring.
Install the upper thread trimmer knife so that
it cuts only one side of the upper thread loop.
Adjust the needle bar height or the
looper and spreader height.
Adjust the amount of upper thread
being fed out.
Grind the hammer surface.
Adjust the cutting pressure so that
it is strong enough.
Replace with a new knife.
Page
60
60
62
72
62
60
60
62
62
62
52
54
59
60
60
73