Brother S-7200B Service Manual page 73

Problem
9 Lower thread is tangled at
the sewing start.
Spinning of bobbin during
thread trimming
10 Upper and lower threads
are breaking.
11 Incorrect thread trimming
(Upper and lower threads
are both not
trimmed)
12 Incorrect thread trimming
(Upper thread or lower
thread is not
trimmed)
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
Lower
wound onto the bobbin?
thread
The
amount should not be
more that 80 %.
the
Is 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 that the light-alloy bobbins specified by Brother
being used?
Use only bobbins which are specified by Brother.
0751M
Is the needle tip bent? Is the needle tip blunt?
If the needle tip is bent or blunt, replace the needle.
Is the needle properly installed?
If it is incorrect, install the needle correctly.
Is the machine properly threaded?
If it is incorrect, thread the thread correctly.
Is the rotary hook sufficiently lubricated? (-[]0[], []3[] specifications)
If the oil gauge is down to the lower reference line in the oil
gauge window, add more oil.
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 take-up spring
operating range is too small?
Adjust the position of the thread take-up spring.
Is the rotary hook, feed dog or other part damaged?
If they are damaged, smooth them with an oiled grindstone or
replace the damaged parts.
Is the thread path damaged?
If the thread path is damaged, smooth it with sandpaper or
replace the damaged part.
0471M
Is the fixed knife or movable knife damaged or worn?
Replace the fixed knife or the movable knife.
being
Is the needle properly installed?
If it is incorrect, install the needle correctly.
being Is the fixed knife or movable knife blunt?
Replace the fixed knife or the movable knife.
Possible cause
bobbin winding
S-7200B
13. TROUBLESHOOTING
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