Brother DB2-B721 - Page 78

13. TROUBLESHOOTING
10.
Problem
Incorrect thread trimming
(upper and lower threads
are both not being
trimmed). (B722/B724)
Incorrect thread trimming
(upper thread or lower
thread is not being
trimmed). (B722/B724)
11. Broken needles
12.
59
/
/
The thread wiper does
not wipe the thread.
(B722/B724-40a 900,
option)
Possible cause
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
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