Troubleshooting Guide; Presser Foot - Brother b831 Service Manual

TROUBLESHOOTING GUIDE
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LT2-B831 B832
B835-8836 8882
Trouble
Thread breaks
Loose threads
Cause Check
Remedy
Damaged rotary hook
holding slot in the needle
plate.
Polish the rotating hook
holding slot.
Improper upper thread
tension.
Upper thread tension.
Refer to "Thread Tension".
Refer to p. 12 of the
supplementary instruction
manual.
Bobbin case opener gap.
Set the rotary hook and
bobbin case opener gap to
0.2 mm.
Improper needle and
rotary hook timing.
Needle and rotary hook
point gap.
Set the needle and rotary
hook point gap to 0.5 mm.
Rotary hook and needle
plate gap.
Needle bar lift stroke and
height
Check that the needle plate
and rotary hook gap is
approx. 1.3 mm.
Adjust the needle bar lift
stroke and height.
Insufficient lubrication to
Rotary hook lubrication
Adjust the lubricating oil
supply to the rotary hook.
Refer to p. 7 of the supple
mentary instruction
manual.
the rotary hook assembly.
Improper thread take-up
Thread take-up spring
Refer to "Thread Tension"
m the supplementary in
struction manual.
spring tension and stroke.
stroke and tension.
Rotary hook point
Polish the rotary hook
damaged.
point.
Damaged needle hole in
the feed dog.
Polish the needle hold in
the feed dog.
Improper threading
Threading
Refer to "Upper Thread
ing .
Improper needle installa
Needle groove direction
Install the needle in the
tion.
proper direction.
Bent or blunt needle
Needle
Refer to the "Thread breaks" section (above). Also check below.
Bobbin sticks.
When using a machine for
medium-thick materials,
the thread does not tighten
properly with some mate
rials.
Replace the needle.
Replace the bobbin.
Replace with a slotted
presser foot (for med. thick
materials).
Replace with a slotted feed
dog (for med. thick mate
rials)