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15. TROUBLESHOOTING
Problem
9.
Lower thread is tangled at the
sewing start.
Lower
thread
Spinning of bobbin
during thread
trimming
10. Upper and lower threads are
breaking.
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).
13. Broken needles
145
● 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
80%
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 re-
place the damaged parts.
● Is the fixed knife or movable knife damaged or worn?
Replace the fixed knife or the movable knife.
● 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 material being pushed or pulled with excessive force during
sewing?
● Is the needle properly installed?
If it is incorrect, install the needle correctly.
● Is the needle bent, is the needle tip broken, or is the needle hole
blocked?
Replace the needle.
● Is the needle and rotary hook timing incorrect?
Adjust the height of the needle bar.
Adjust the clearance between the needle and the rotary hook.
● Is the needle timing advanced too far with respect to the feed dog?
Retard the needle timing.
Caution
● It is extremely dangerous to leave any pieces of broken needle
sticking in the material. If the needle breaks, search for all pieces
until the whole of the needle is found again.
● Furthermore, we recommend that through steps be taken to ac-
count for such needles to comply with product liability regula-
tions.
Possible cause
DB2-DD7100A
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