Brother T-8421B Instructions Manual page 54

11. TROUBLESHOOTING
Problem
5 Uneven seam
6 Large degree of puckering
(excess tension)
7 Material slippage
8 Lower thread is tangled at
the sewing start.
Spinning of bobbin during
thread trimming
47
y Is the presser foot pressure too weak?
Adjust the presser foot pressure.
y Is the feed dog too low?
Adjust the feed dog height.
y Is the bobbin scratched?
If the bobbin is damaged, smooth it with an oiled grindstone or
replace it.
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y Is the upper thread tension too strong?
Make the upper thread tension as weak as possible.
y Is the lower thread tension too strong?
Make the lower thread tension as weak as possible.
y Are the thread take-up spring tensions too strong?
Make the thread take-up spring tension as weak as possible.
y Is the thread take-up spring operating range too large?
Move the stopper to as high a position as possible.
y Is the presser foot pressure too strong?
Adjust the presser foot pressure.
y Is the sewing speed too fast?
Use the sewing speed control keys to gradually reduce the
sewing speed.
y Is the thread take-up amount too small?
Adjust the thread take-up amount.
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y Is the presser foot pressure too strong?
Adjust the presser foot pressure.
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y Is the bobbin spinning direction correct when the lower thread is
being pulled?
Set the bobbin so that it turns in the opposite direction to the
rotary hook.
y Is there too much thread
wound onto the bobbin?
Lower
The bobbin
thread
amount should not be
more that 80 %.
y Is
the
anti-spin spring attached? (Models with thread trimmer)
Attach the anti-spin spring.
y Is the bobbin turning smoothly?
If the bobbin is not turning smoothly, replace the bobbin.
y Is a bobbin other that the light-alloy bobbins specified by Brother
being used?
Use only bobbins which are specified by Brother.
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T-8421B, 8422B, 8452B, 8722B, 8752B
Possible cause
winding
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