Brother LZ2-B850 Service Manual page 39

Problem
5. Uneven seam
6. Horizontal thread tightening
not balanced
Upper thread
Lower thread
7. Large degree of puckering
(excess tension)
• Is the presser foot pressure too weak?
Adjuste the presser foot pressure.
• Is the feed dog too low?
Adjust the feed dog height.
• Is the bobbin scratched?
If the bobbin is damaged, smooth it with an oiled grindstone
or replace it.
0625M
• Is the upper thread tension or lower thread tension too strong
or to weak?
Adjust the upper thread tension or lower thread tension.
• Does the rotary disc rotate smoothly?
Adjust the pre-tension.
• Is the tension of the thread take-up spring correct?
Adjust the tension of the thread take-up spring.
• Is the stroke of the thread take-up spring correct?
Adjust the position of the thread take-up spring.
• Is the needle and rotary hook timing correct?
Adjust the needle and rotary hook timing.
• Is the needle and rotary hook timing correct?
Adjust the height of the needle bar.
Adjust the clearance between the needle and the rotary hook.
• 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.
0626M
• 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.
• Is the point of the needle broken?
If the point of the needle is broken, replace the needle.
• Is the needle too thick?
Replace with as thin a needle as possible.
• Are the thread take-up spring tensions too strong?
Make the thread take-up spring tension as weak as possible.
• Is the thread tension spring operating range too large?
Lower the position of the thread tension spring to as low a po-
sition as possible.
• Is the presser foot pressure too strong?
Adjust the presser foot pressure.
• Is the sewing machine running too fast?
Check that an appropriate motor pulley (outer diameter) which
matches the maximum sewing speed and the frequency is
being used. If an incorrect motor pulley is being used, replace
the motor pulley.
• Is the angle of the feed dog incorrect?
Tilt the front of the feed dog down slightly.
0627M
Possible cause
LZ2-B850,B851
6. TROUBLESHOOTING
Page
—
5-02
—
—
—
5-01
5-01
5-05
5-06
5-12
—
—
—
—
—
—
5-01
5-01
—
1-02
5-03
6-02