Troubleshooting; Sewing - Brother T-8421B Instructions Manual

11. TROUBLESHOOTING

11. TROUBLESHOOTING
y Please check the following points before calling for repairs or service.
y 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 face plate of the control box. 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 troubleshooting.
The machine may operate if the treadle is depressed by mistake, which could result in injury.

11-1. Sewing

Items with a "*" in the "Page" column should only be checked by a qualified technician.
Problem
1 Upper thread is not tight.
Lower thread is not tight.
0574M 0573M
2 Loops appear in seam.
45
y Has the thread been threaded incorrectly?
If the thread is threaded incorrectly, thread it correctly.
y Is the upper thread tension or lower thread tension too weak?
Adjust the upper thread tension or lower thread tension.
y 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.
y Is the thread path not smooth enough?
Use a file with a fine grain or sandpaper to polish smooth the
thread path.
y Is the bobbin not turning smoothly?
Pull out the lower thread to check that there is no slackness in
the thread tension, or replace the bobbin or bobbin case.
y Is the thread take-up amount too large?
Adjust the thread take-up amount.
0977M
T-8421B, 8422B, 8452B, 8722B, 8752B
DANGER
CAUTION
Possible cause
Slot
Page
18-22
35
*
Grooves
2944M
38