Brother LZ2-B850 Service Manual page 40

6. TROUBLESHOOTING
Problem
8. Lower thread is tangled at
the sewing start.
Lower thread
80%
9. Upper and lower threads
are breaking.
10. Broken needles
6-03
• 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 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?
0628M Use only bobbins which are specified by Brother.
0629M
• 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 needle and rotary hock timing incorrect?
Adjust the height of the needle bar.
Adjust the clearance between the needle and the rotary hock.
• Is the thread too thick for the needle?
Use the correct needle or the correct thread.
• Is the rotary hook, bobbin case, thread take-up lever or some
other part in the thread path damaged?
Repair the damage, or replace the part with a new one.
0471M
• Is the material being pushed or pulled with excessive force dur-
ing sewing?
• Is the needle properly installed?
If it is incorrect, install the needle correctly.
• Is the needle bent, is the needle tip broken, or is the needle
hole blocked?
Replace the needle.
• Is the needle and rotary hook timing incorrect?
Adjust the height of the needle bar.
Adjust the clearance between the needle and the rotary hook.
Caution
• It is extremely dangerous to leave any pieces of broken
needle sticking in the material. If the needle breaks, search
for all pieces until the whole of the needle is found again.
• Furthermore, we recommend that through steps be taken
to account for such needles to comply with product liability
regulations.
0469M
Possible cause
LZ2-B850,B851
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