Brother International T-8420B Instruction Manual - English - Page 40

Troubleshooting

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10. TROUBLESHOOTING 10. 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. CAUTION Turn off the power switch and disconnect the power cord before carrying out troubleshooting. 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. The machine may operate if the treadle is depressed by mistake, which could result in injury. Items with a "*" in the "Page" column should only be checked by a qualified technician. Problem Possible cause 1 Machine does not operate y Is a breaker or fuse blown? when power is turned on y Is the power cord disconnected? and treadle is pressed. y Is the V-belt installed? 2 Upper thread is not tight. 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. Lower thread is not tight. 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. Grooves Slot Page * 7 16-20 25 * 0573M 0574M 2944M 3 Loops appear in seam. 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. 27 0977M T-8420B, 8450B, 8720B, 8750B 34

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T-8420B, 8450B, 8720B, 8750B
10. TROUBLESHOOTING
34
10. TROUBLESHOOTING
Please check the following points before calling for repairs or service.
If the following remedies do not fix the problem, turn off the power switch and consult a qualified technician or the place of
purchase.
CAUTION
Turn off the power switch and disconnect the power cord before carrying out troubleshooting. 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.
The machine may operate if the treadle is depressed by mistake, which could result in injury.
Items with a “*” in the “Page” column should only be checked by a qualified technician.
Problem
Possible cause
Page
1
Machine does not operate
when power is turned on
and treadle is pressed.
Is a breaker or fuse blown?
Is the power cord disconnected?
Is the V-belt installed?
*
7
2
Upper thread is not tight.
Lower thread is not tight.
Has the thread been threaded incorrectly?
If the thread is threaded incorrectly, thread it correctly.
Is the upper thread tension or lower thread tension too weak?
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.
16-20
25
*
3
Loops appear in seam.
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 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.
Is the thread take-up amount too large?
Adjust the thread take-up amount.
27
0573M
0574M
0977M
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.
2944M
Slot
Grooves