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15. TROUBLESHOOTING
Problem
7. Material slippage
8. Lower thread is tangled at
the sewing start.
Lower
thread
Spinning of bobbin
during thread trimming (B772A)
80%
9. Upper and lower threads are
breaking.
10. Incorrect thread trimming
(upper and lower threads
are both not being
trimmed). (B772A)
63
¡ Is the presser foot pressure too strong?
Adjust the presser foot pressure.
¡ Is the angle of the feed dog incorrect?
Tilt the front of the feed dog up slightly.
¡ Is the needle and feed mechanism timing correct?
Retard the needle timing.
0750M
¡ 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%.
¡ Is the anti-spin spring attached?
Attach the anti-spin 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
0751M
being used?
Use only bobbins which are specified by Brother.
0752M
¡ Is the needle bent or is the needle tip broken?
Replace the needle if it is bent or broken.
¡ Is the needle properly installed?
If it is incorrect, install the needle correctly.
¡ Is the needle properly threaded?
If it is incorrect, thread the needle correctly.
¡ 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.
0471M
¡ Is the fixed knife or movable knife damaged or worn?
Replace the fixed knife or the movable knife.
Possible cause
DB2-B771A, B772A
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