Brother DB2-B721 - Troubleshooting

13. TROUBLESHOOTING
13. TROUBLESHOOTING
• Please check the following points before calling for repairs or service.
• If the following suggestions do not solve the problem, turn off the machine power supply and contact your nearest
Brother service center.
A
A CAUTION
Turn off the power switch and disconnect the power cord before carrying out troubleshooting, otherwise
the machine will operate if the treadle is pressed by mistake, which could result in injury.
* When using a clutch motor, the motor will keep turning even after the power is switched off as a result
of the motor's inertia. Wait until the motor stops fully before starting work.
Problem
Possible cause
Page
1. Upper thread is not tight.
• Is the upper thread tension too weak, or is the lower thread tension
too strong?
Adjust the upper thread tension or lower thread tension.
31
• Is the needle and feed mechanism timing correct?
Advance the needle timing.
47
• Is the lower thread tension too weak, or is the upper thread tension
too strong?
Adjust the lower thread tension or upper thread tension.
31
3. Skipped stitches occur while
sewing
• Is the needle tip bent? Is the needle tip blunt?
If the needle tip is bent or broken, replace the needle.
—
• Is the needle properly installed?
If it is incorrect, install the needle correctly.
21
• Is the machine properly threaded?
If it is incorrect, thread the thread correctly.
25-26
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• Is the presser foot pressure too weak?
Adjust the presser foot pressure.
32
• Is the needle too thin?
Replace the needle with a needle that is one rank thicker.
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• Is the presser foot too high?
Adjust the height of the presser foot.
43
• 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.
46
49
• Is the thread tension spring too weak?
Adjust the tension of the thread tension spring.
41
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DB2-B720 series
56