Brother DB2-DD7100, Service Manual

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22. TROUBLESHOOTING
SL-710A
138
Problem Possible cause Page
9. Lower thread is tangled
at the sewing start.
Spinning of bobbin
during thread trimming
•
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.
Instruction manual
Instruction manual
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10.Upper and lower
threads are breaking.
•
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.
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Instruction manual
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Instruction manual
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48, 49
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11. Incorrect thread trimming.
(upper and lower
threads are both not
being trimmed).
•
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.
Instruction manual
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104
12. Incorrect thread trimming.
(upper thread or
lower thread is not
being trimmed).
•
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.
Instruction manual
Instruction manual
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80%
Lower
thread
0471M
0801M
0751M