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17. 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.
Disconnect the air hoses from the air supply and wait for the needle on the pressure gauge to drop to "0" before
carrying out inspection adjustment and repair of any parts which use the pneumatic equipment.
17-1. Machine head
Problem
1. Upper thread is not tight.
2. Lower thread is not tight.
3. Loops appear in seam.
CAUTION
Is the upper thraed tension too weak, or is the lower thread tension too
strong?
Adjust the upper thread tension or lower thread tension.
Is the thread tension spring too weak?
Adjust the tension of the thread tension spring.
Is the operating range for the thread take-up spring too small?
Increase the operating range for the thread take-up spring.
Is the clearance between the needle plate and the inner rotary hook stop-
per correct?
Adjust the position of the opener.
Is the lower thread tension too weak, or is the upper thread tension too
strong?
Adjust the lower thread tension or upper thread tension.
Is the tip of the needle burred?
If the tip of the needle is burred, replace the needle.
Is the needle hole facing in the correct direction?
If the direction of the hole is incorrect, install the needle correctly.
Is the needle too thin for the thread?
Replace with a needle which is one rank thicker.
Is the upper thread tension too weak?
Adjust the upper thread tension.
Is the thread tension spring too weak?
Adjust the tension of the thread tension spring.
Is the operating range for the thread take-up spring too small?
Increase the operating range for the thread take-up spring.
Is the thread path not smooth enough?
Use a file with a fine grain or sandpaper to polish smooth the thread path.
Is there too much thread wound onto the bobbin?
The bobbin winding amount should not be more than 80%.
Is the bobbin winding tension too strong or too weak?
Wind the thread onto the bobbin at an appropriate tension.
LS2-B891, LT2-B892
Possible cause
17. TROUBLESHOOTING
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