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13. TROUBLESHOOTING
Problem
09. Incorrect thread trimming
(upper and lower threads
are both not being
trimmed). (B722/B724)
10. Incorrect thread trimming
(upper thread or lower
thread is not being
trimmed). (B722/B724)
11. Broken needles
12. The thread wiper does
not wipe the thread.
(B722/B724-40M, 90M,
option)
59
¡
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.
¡
Is the length of thread trailing from the needle hole too long after
thread trimming?
Adjust the pretension.
DB2-B720 series
Possible cause
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