Brother T-8420C Instruction Manual page 56

11. TROUBLESHOOTING
Problem
6 Uneven seam
7 Large degree of puckering
(excess tension)
8 Material slippage
9 Lower thread is tangled at
the sewing start.
47
y Is the presser foot pressure too weak?
Adjust the presser foot pressure.
y Is the feed dog too low?
Adjust the feed dog height.
y Is the bobbin scratched?
If the bobbin is damaged, smooth it with an oiled grindstone or
replace it.
y Is the V-belt tension too low?
Adjust so that there is 10-14 mm of deflection in the V-belt
when it is pushed with a finger.
2948M
y Is the upper thread tension too strong?
Make the upper thread tension as weak as possible.
y Is the lower thread tension too strong?
Make the lower thread tension as weak as possible.
y Are the thread take-up spring tensions too strong?
Make the thread take-up spring tension as weak as possible.
y Is the thread take-up spring operating range too large?
Move the stopper to as high a position as possible.
y Is the presser foot pressure too strong?
Adjust the presser foot pressure.
y Is the thread take-up amount too small?
Adjust the thread take-up amount.
2949M
y Is the presser foot pressure too strong?
Adjust the presser foot pressure.
2949M
2950M
y 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.
y Is there too much thread
wound onto the bobbin?
Lower
The bobbin
thread
amount should not be
more that 80 %.
y Is the bobbin turning smoothly?
If the bobbin is not turning smoothly, replace the bobbin.
y Is a bobbin other that the light-alloy bobbins specified by Brother
being used?
Use only bobbins which are specified by Brother.
2951M
T-8420C, 8450C, 8720C, 8750C
Possible cause
winding
Page
26
43*
7
25
25
36*
35*
26
28
26
17 18
•
16
17 18
•
2124M