Troubleshooting; Troubleshooting During Sewing - Brother T-8421D Instruction Manual

9

Troubleshooting

• Please check the following points before calling for repairs or service.
• Simplified details can be checked on the panel.
• If the following remedies do not fix the problem, turn off the power switch and consult a qualified technician or
the place of purchase.
• Wait at least 5 minutes after turning off the power switch and disconnecting the power cord from the
wall outlet before opening the control box cover. Touching areas where high voltages are present
can result in severe injury.
• Turn off the power switch and disconnect the power cord before carrying out these operations. The
machine may operate if the treadle is depressed by mistake, which could result in injury.

Troubleshooting during sewing

Items with a "*" in the "Page" column should only be checked by a qualified technician.
Problem
Upper thread is not tight.
Lower thread is not tight.
Loops appear in seam.
DANGER
CAUTION
Possible cause
• Is the machine properly threaded?
If it is incorrect, thread the thread correctly.
• Is the upper thread tension too weak? Or is the lower
thread tension too strong?
Adjust the upper thread tension or lower thread
tension.
• Is the thread take-up spring operating range too
small?
Lower the position of the stopper.
• If using a sewing machine with medium-weight
material specifications, poor thread tightening may
occur depending on the type of material being sewn.
In such cases, replace the presser foot with one that
has slots on the underside. Or replace the feed dog
with a grooved feed dog.
• Is the thread path not smooth enough?
Use a file with a fine grain or sandpaper to polish
smooth the thread path.
• Is the bobbin turning smoothly?
Page
See Threading the upper
thread on page 22.
See Adjusting the thread
tension on page 62.
See Adjusting the thread
take-up amounts of the
thread tension springs on
1
page 74.
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