Troubleshooting - Brother LZ2-B850 Service Manual

6. TROUBLESHOOTING

6. 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.
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
1. Upper thread is not tight.
2. Lower thread is not tight.
3. Skipped stitches occur
while sewing
4. Skipped stitches at sewing
start
Thread unravelling at
sewing start
Upper thread
q
6-01
CAUTION
• Is the upper thread tension too weak, or is the lower thread
tension too strong?
Adjust the upper thread tension or lower thread tension.
0573M
• Is the lower thread tension too weak, or is the upper thread
tension too strong?
Adjust the lower thread tension or upper thread tension.
0574M
• 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.
• Is the machine properly threaded?
If it is incorrect, thread the thread correctly.
• Is the presser foot pressure too weak?
Adjust the presser foot pressure.
• Is the needle too thin?
Replace the needle with a needle that is one rank thicker.
• Is the presser foot too high?
Adjust the height of the presser foot.
• 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 thread tension spring too weak?
Adjust the tension of the thread tension spring.
0621M
• Are the thread take-up spring tensions too strong?
Reduce the tension of the thread take-up springs.
• Is the thread tension spring operating range too large?
Lower the position of the thread tension spring.
• Is the needle too wide?
Try using a needle with a count that is one lower than the cur-
0622M rent needle.
Is the reference line q on the machine pulley aligned with the
•
mark on the belt cover at the sewing start...
Align the reference line q on the machine pulley with the mark
on the belt cover at the sewing start.
• Is the length of thread trailing out from the needle hole too
short?
Align the reference line q on the machine pulley with the mark
on the belt cover at the sewing start, and then pull out 50 mm
of thread from the needle hole.
0623M
0624M
Possible cause
LZ2-B850,B851
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