Brother T-8421B Instructions Manual page 53

3 Skipped stitches occur
while sewing
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4 Skipped stitches at sewing
start
Thread unravelling
sewing start
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y Is the needle tip bent? Is the needle tip blunt?
If the needle tip is bent or broken, replace the needle.
y Is the needle properly installed?
If it is incorrect, install the needle correctly.
y Is the machine properly threaded?
If it is incorrect, thread the thread correctly.
y Is the presser foot pressure too weak?
Adjust the presser foot pressure.
y Is the needle too thin?
Replace the needle with a needle that is one rank thicker.
y Is the presser foot too high?
Adjust the height of the presser foot.
y Is the thread take-up spring too weak?
Adjust the tension of the thread take-up spring.
y Is the thread take-up amount too large?
Adjust the thread take-up amount.
y Is the thread take-up spring tension too strong?
Reduce the tension of the thread take-up spring.
y Is the thread take-up spring operating range too large?
at
Raise the position of the stopper.
y Are the trailing lengths of the upper threads too short after thread
trimming?
Adjust the pretension.
y Are the threads not being trimmed cleanly?
Sharpen the fixed knives, or replace the fixed and movable
knives if necessary.
y Is the needle too wide?
Try using a needle with a count that is one lower than the
current needle.
y Is the sewing speed too fast at the sewing start?
Use the slow start feature.
y Is the needle up stop position too high?
Adjust the needle up stop position.
y Is the lower thread pressed by the plate spring (1) after thread
trimming?
If the lower thread is not
pressed by the plate spring
(1), adjust the installation
position of the movable
knife (2).
y If sewing light or medium-weight materials, is a presser foot with
slots on the underside or grooved feed dog being used?
Use a presser foot without slots.
Use a feed dog without grooves.
T-8421B, 8422B, 8452B, 8722B, 8752B
Lower thread
Slot
11. TROUBLESHOOTING
16
18-22
36
*
*
38
*
*
37
*
30
31
*
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Grooves
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46