Brother T-8420B Instruction Manual page 42

Problem
6 Uneven seam
7 Large degree of puckering
(excess tension)
8 Material slippage
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9 Lower thread is tangled at
the sewing start.
Lower
thread
Is the presser foot pressure too weak?
Adjust the presser foot pressure.
Is the feed dog too low?
Adjust the feed dog height.
Is the bobbin scratched?
If the bobbin is damaged, smooth it with an oiled grindstone or
replace it.
Is the V-belt tension too low?
Adjust so that there is 10-14 mm of deflection in the V-belt
when it is pushed with a finger.
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Is the upper thread tension too strong?
Make the upper thread tension as weak as possible.
Is the lower thread tension too strong?
Make the lower thread tension as weak as possible.
Are the thread take-up spring tensions too strong?
Make the thread take-up spring tension as weak as possible.
Is the thread take-up spring operating range too large?
Move the stopper to as high a position as possible.
Is the presser foot pressure too strong?
Adjust the presser foot pressure.
Is the thread take-up amount too small?
Adjust the thread take-up amount.
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Is the presser foot pressure too strong?
Adjust the presser foot pressure.
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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.
Is there too much thread
wound onto the bobbin?
The bobbin
amount should not be
more that 80 %.
Is the bobbin turning smoothly?
If the bobbin is not turning smoothly, replace the bobbin.
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-8420B, 8450B, 8720B, 8750B
Possible cause
winding
10. TROUBLESHOOTING
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