Owner's Manual

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14. TROUBLESHOOTING GUIDE
14. FEHLERSUCHE
14. RECHERCHES DE PANNES
14. GUIA PARA LA LOCALIZACION DE FALLAS
TN-840B, 870B (English)
TL-840B (English)
Problem Where to check Page
51
51
65
66
52
Motor
instruc-
tion
manual
¡ Is the timing correct during thread trimming?
Adjust the timing for thread trimming.
¡ Are the tips of the movable knives damaged or bent?
Replace the movable knife which is damaged.
¡ Is there too much clearance between the tips of the movable knives
and the rotary hook stoppers?
Adjust so that the clearance is 0.05–0.2 mm.
¡ Is the tension release mechanism working correctly?
Adjust the tension release mechanism.
¡ Are the tips of the movable knives in the correct positions?
Adjust the positions of the movable knives.
85 · 86
78
79
81
79
7. Upper thread trimming
errors
6. Large degree of puckering
(excess tension)
¡ Is the upper thread tension too strong?
Make the upper thread tension as weak as possible.
¡ Is the lower thread tension too strong?
Make the lower thread tension as weak as possible.
¡ Are the thread take-up spring tensions too strong?
Make the thread take-up spring tension as weak as possible.
¡ Are the ranges of movement for the thread take-up springs too large?
Make the ranges of movement of the thread take-up springs as small
as possible.
¡ Is the presser foot pressure too weak?
Increase the presser foot pressure.
¡ Is the sewing speed too fast?
Reduce the sewing speed slightly.
8. Lower thread trimming
errors
¡ Are the tips of the movable knives too low?
Are the tips of the movable knives damaged or bent?
Replace the movable knife which is damaged.
¡ Are the rotary hooks too high?
Push the rotary hooks down to install them correctly.
78
68
9. Lower thread is tangled at
the sewing start.
¡ Is the bobbin spinning direction correct when the lower thread is
being pulled?
Set the bobbin so that it turns in the opposite direction to the rotary
hook.
¡ Is there too much thread wound onto the bobbin?
The bobbin winding amount should not be more than 80%.
¡ Is the free spinning prevention spring attached?
Attach the free spinning prevention spring.
¡ Is the bobbin turning smoothly?
If the bobbin is not turning smoothly, replace the bobbin.
¡ Is a bobbin other than the light-alloy bobbins specified by Brother
being used?
Use only bobbins which are specified by Brother.
41 · 42
38
40
40
Lower
thread
80%
Spinning of bobbin
during thread
trimming