Brother Z-8550A Service Manual page 120

14. TROUBLESHOOTING
Problem
6 Uneven seam
7 Horizontal thread tighten-
ing not balanced
Lower
thread
8
Large degree of puckering
(excess tension)
111
• Is the presser foot pressure too weak?
Adjust 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
too weak?
Adjust the upper thread tension or lower thread tension.
Upper
• Does the rotary disc rotate smoothly?
thread
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 operating range of the thread take-up spring correct?
Adjust the position of the thread take-up spring.
• 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.
• 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 take-up spring operating range too large?
Lower the position of the thread take-up spring to as low a
position as possible.
• Is the presser foot pressure too strong?
Adjust the presser foot pressure.
• Is the sewing speed too fast?
Use the sewing speed control keys to gradually reduce the
sewing speed.
• Is the angle of the feed dog incorrect?
Tilt the front of the feed dog down slightly.
0627M
Possible cause
Z-8550A, 8560A
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Instruction
manual
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Instruction
manual
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