Brother ZM-851A Instruction Manual page 89

Problem
4. Skipped stitches at sewing
start
Thread unravelling at
sewing start
Upper thread
q
5. Uneven seam
6. Horizontal thread tightening
not balanced
Upper thread
Lower thread
• Are the thread take-up spring tensions too strong?
Reduce the tension of the thread take-up springs.
• Is the thread tension spring operating range too large?
Lower the position of the thread tension spring.
• Is the needle too wide?
Try using a needle with a count that is one lower than the cur-
rent needle.
Is the reference line q on the machine pulley aligned with the
•
mark on the belt cover at the sewing start?
Align the reference line q on the machine pulley with the mark
0622M
on the belt cover at the sewing start.
• Is the length of thread trailing out from the needle hole too
short?
Align the reference line q on the machine pulley with the mark
on the belt cover at the sewing start, and then pull out 50 mm
of thread from the needle hole.
0623M
0624M
• 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
Possible cause
ZM-850A, 851A
12. TROUBLESHOOTING
12. FEHLERSUCHE
12. RESOLUTION DES PROBLEMES
12. LOCALIZACION DE AVERIAS
Page
48
47
—
27
28
41
50
—
39
40
48
47
57
55
57
—
—
70