Brother S-710A Service Manual page 145

Problem
9. Lower thread is tangled
at the sewing start.
Spinning of bobbin
during thread trimming
Lower
thread
0751M
80%
0801M
10.Upper and lower
threads are breaking.
0471M
11. Incorrect thread trimming.
(upper and lower
threads are both not
being trimmed).
12. Incorrect thread trimming.
(upper thread or
lower thread is not
being 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 wound onto the bobbin?
The bobbin winding amount should not be more than 80%.
• Is the free spinning prevention spring attached?
Attach the free spinning prevention 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?
Use only bobbins which are specified by Brother.
• 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 rotary hook sufficiently lubricated?
If the oil gauge is down to the lower reference line in the oil sight glass,
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 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 replace
the damaged parts.
• Is the thread path damaged?
If the thread path is damaged, smooth it with sandpaper, or replace the
damaged part.
• Is the fixed knife or movable knife damaged or worm?
Replace the fixed knife or the movable knife.
• Is the fixed knife and movable knife meshing amount correct?
Adjust the fixed knife and movable knife meshing amount.
• Is the movable knife operating correctly?
Measure the resistance between terminals 3-4 of the sewing machine
connector with an ohmmeter. If the measured value is not normal,
replace the thread trimmer solenoid.
• Is the needle properly installed?
If it is incorrect, install the needle correctly.
• Is the fixed knife or movable knife blunt?
Replace the fixed knife or the movable knife.
• Is the fixed knife and movable knife meshing amount correct?
Adjust the fixed knife and movable knife meshing amount.
Possible cause
SL-710A
22. TROUBLESHOOTING
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