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13. TROUBLESHOOTING
Problem
7. Large degree of puckering
(excess tension)
8. Lower thread is tangled at
the sewing start.
Lower
thread
Spinning of bobbin
during thread trimming (748A)
80%
9. Upper and lower threads
are breaking.
55
All manuals and user guides at all-guides.com
¡
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.
¡
Is the point of the needle broken?
If the point of the needle is broken, replace the needle.
¡
Is the needle too thick?
Replace with as thin a needle 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 tension spring operating range too large?
Lower the position of the thread tension spring to as low a position
as possible.
¡
Is the presser foot pressure too strong?
Adjust the presser foot pressure.
¡
Is the sewing speed too fast?
Reduce the sewing speed slightly.
¡
Is the angle of the feed dog incorrect?
Tilt the front of the feed dog down slightly.
¡
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 winding amount should not be more than 80%.
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Is the bobbin tension spring attached? (748A)
Attach the bobbin tension spring.
¡
Is the bobbin turning smoothly?
If the bobbin is not turning smoothly, replace the bobbin.
¡
Is a bobbin other than the light-alloy bobbins specified by Brother
being used? (748A)
Use only bobbins which are specified by Brother.
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Is the needle bent or is the needle tip broken?
Replace the needle if it is bent or broken.
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Is the needle properly installed?
If it is incorrect, install the needle correctly.
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Is the needle properly threaded?
If it is incorrect, thread the needle correctly.
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Is the upper or lower thread tension too weak or too strong?
Adjust the upper thread or lower thread tension.
¡
Is the upper thread may be loose because the thread tension spring
operating range is too small?
Adjust the position of the thread tension spring.
¡
Is the rotary hook, feed dog or other part damaged?
If they are damaged, smooth them with an oiled grindstone or re-
place the damaged parts.
SL-746A, 748A
Possible cause
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