Lower Thread Is Not Trimmed (Pulls When Material Is Removed); Feed Mechanism Does Not Operate Or Motor Is Out Of Step - Brother LH4-B800E Service Manual

5-16. Lower thread is not trimmed (pulls when material is removed)

Cause
Machine Rotary hook and lower
stopping thread retainer touch at
position the stop position.
Fixed knife Fixed knife and
set movable knife do not
mesh.
Knife tip is bent or
chipped.

5-17. Feed mechanism does not operate or motor is out of step

Cause
Feed pulse Cord connection
motor
Upper thread Upper thread scissors
scissors position
Is the cam opening the
stop plate?
Feed home Feed home position
position sensor position
sensor
Feed timming Feed timing belt
belt tension
Check
Refer to "5-15. Folding clamp is not raised"
Adjust the fixed knife
set installation position.
Repair or replace the
knife.
Check
Check the cord
connections and
contacts.
Remove and re-install
the upper thread
scissors.
If the feed mechanism
operates when the cam
has not opened the
stop plate, the feed
mechanism will go out
of step and the cutter
will bump against the
upper thread scissors.
Adjust the cam
position.
Adjust the feed home
position sensor
position.
Adjust the feed timing
belt.
Solution
Refer to "4-14-1. Adjusting the lower thread
trimmer fixed knife engagement amount"
Solution
Projection on scissors M is inserted.
* Always make sure that the upper
thread scissors are in the correct
position before us.
NG
LH4-B800E
5. Troubleshooting guide
page
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page
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4-14
4-17
4-18
O.K.
4-3
4-26
5 - 17