Brother BAS-311F-0 Instruction Manual page 76

Problem
Upper thread breaks.
Lower thread breaks.
Skipped stitches occur.
Needle breaks.
Cause
Upper thread tension is
too strong.
Needle is installed
incorrectly.
Thread is too thick for
the needle.
Thread take-up spring
tension and height are
incorrect.
Damaged or burred
rotary hook, needle hole
plate or needle.
Thread melting
(synthetic thread)
Thread path is incorrect.
Lower thread tension is
too strong.
Corners of needle hole
plate or bobbin case
are damaged.
Clearance between needle
and rotary hook tip is too
great.
Incorrect needle and
rotary hook timing.
Driver is contacting needle
more than is necessary.
Needle is bent.
Needle is installed
incorrectly.
Needle is touching the
rotary hook.
Needle is bent.
Needle moves about.
Needle is too thin.
BAS-311F-0, 311F-L, 326F-0
Check
Upper thread tension
Needle direction
Thread and needle
Thread take-up spring
tension and height
Damage or burring
Thread edge
Thread
Lower thread tension
Damage
Needle clearance
Needle bar lift amount
Clearance between
driver and needle
Bent needle
Needle direction
Needle clearance
Needle bar lift amount
Bent needle
Needle and thread
Needle and thread
14. TROUBLESHOOTING
Remedy
Adjust the upper thread
tension.
Install the needle so that the
groove is facing forward.
Use the correct thread
for the needle.
Adjust the tension and
height of the thread take-
up spring.
File smooth or replace
the affected part.
Use a thread cooling
device.
Pass the thread correctly
along the thread path.
Adjust the lower thread
tension.
File smooth or replace
the affected part.
Adjust the needle clearance.
the affected part.
Adjust the needle bar lift
amount.
Adjust the driver needle
guard.
Replace the needle.
Install the needle so that the
groove is facing forward.
Adjust the needle clearance.
the groove is facing forward.
Adjust the needle bar lift
amount.
Replace the needle.
Select the correct needle for
the sewing conditions.
Reduce the sewing speed
Use the correct needle
for the material.
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