Brother T-8421D Instruction Manual page 101

Problem
Loops appear in seam.
Skipped stitches occur
while sewing
Skipped stitches at sewing
start
Thread unraveling at
sewing start.
These items should only be investigated by a technician with the proper training.
1
Possible cause
Pull out the lower thread to check that there is no
slackness in the thread tension, or replace the
bobbin or bobbin case.
• Is the thread take-up amount too large?
Adjust the thread take-up amount.
• Is the needle tip bent? Is the needle tip blunt?
If the needle tip is bent or blunt, replace the needle.
• Is the needle properly installed?
If it is incorrect, install the needle correctly.
• Is the machine properly threaded?
If it is incorrect, thread the thread correctly.
• Is the presser foot pressure too weak?
Adjust the presser foot pressure.
• Is the needle too thin?
Replace the needle with a needle that is one rank
thicker.
• Is the presser foot too high?
Adjust the height of the presser foot.
• Is the thread take-up spring too weak?
Adjust the tension of the thread take-up spring.
• Is the thread take-up amount too large?
Adjust the thread take-up amount.
• Is the thread take-up spring tension too strong?
Reduce the tension of the thread take-up spring.
• Is the thread take-up spring operating range too
large?
Lower the position of the stopper.
• Is the needle too thick?
Replace the needle with a needle that is one rank
thinner.
(T-8422D/T-8452D/T-8722D/T-8752D)
• Is the trailing length of the upper thread too short
after thread trimming?
Adjust the pretension.
(T-8422D/T-8452D/T-8722D/T-8752D)
• Are the threads not being trimmed cleanly?
Sharpen the fixed knives, or replace the fixed and
movable knives if necessary.
Replace the movable knife.
1
1
1
1
1
Page
See Adjusting the thread
take-up amount on
page 66.
See Installing the needle
on page 17.
See Installing the needle
on page 17.
See Threading the upper
thread on page 22.
See Adjusting the upper
roller pressure on page 63.
See Adjusting the height of
the presser foot on
page 77.
See Adjusting the tension
of the thread tension spring
1
on page 75.
See Adjusting the thread
take-up amount on
page 66.
See Adjusting the tension
of the thread tension spring
1
on page 75.
See Adjusting the thread
take-up amounts of the
thread tension springs on
page 74.
See Adjusting the upper
thread trailing length after
thread trimming on
page 65.
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