Brother LK3-B434E MKII Instruction Manual page 72

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)
Lower thread tension
is too strong.
Corners of needle
hole plate or bobbin
care 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 is too thin.
LK3-B434E Mark II
Check
Upper thread tension
Needle direction
Thread and needle
Thread take-up
spring tension and
height
Damage or burring
Thread edge
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
17. 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 afffected
part.
Use a thread cooling
device (optional).
Adjust the lower
thread tension.
File smooth or
replace the affected
part.
Adjust the needle
clearance.
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.
Adjust the needle bar
lift amount.
Replace the needle.
Use the correct
needle for the
material.
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