DB2-B727, B728
58
Problem
Possible cause
Page
12. TROUBLESHOOTING
7. 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 bobbin tension spring attached? (B728)
Attach the bobbin tension 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? (B728)
Use only bobbins which are specified by Brother.
22
20
19
–
–
–
18
22 · 23
27
39
–
Lower
thread
80%
Spinning of bobbin during
thread trimming (B728)
8. Upper and lower threads
are breaking.
¡
Is the needle bent or is the needle tip broken?
Replace the needle if it is bent or broken.
¡
Is the needle properly installed?
If it is incorrect, install the needle correctly.
¡
Is the needle properly threaded?
If it is incorrect, thread the needle correctly.
¡
Is the upper or lower thread tension too weak or too strong?
Adjust the upper thread or lower thread tension.
¡
Is the upper thread may be loose because the thread tension spring
operating range is too small?
Adjust the position of the thread tension spring.
¡
Is the rotary hook, feed dog or other part damaged?
If they are damaged, smooth them with an oiled grindstone or re-
place the damaged parts.
51
18
50
9. Incorrect thread trimming
(upper and lower threads
are both not being
trimmed). (B728)
¡
Is the fixed knife or movable knife damaged or worn?
Replace the fixed knife or the movable knife.
10. Incorrect thread trimming
(upper thread or lower
thread is not being
trimmed). (B728)
¡
Is the needle properly installed?
If it is incorrect, install the needle correctly.
¡
Is the fixed knife or movable knife blunt?
Replace the fixed knife or the movable knife.
0751M
0471M
0752M
