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Problem
4. Skipped stitches at sewing
start
0749M
Thread unravelling at
sewing start
Upper
thread
0623M
5. Uneven seam
0473M
6. Material slippage
0750M
All manuals and user guides at all-guides.com
¡
Is the thread tension spring too strong?
Reduce the tension of the thread tension 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 current
needle.
<B727>
¡
Is the thread take-up lever at its highest position at the sewing start?
Set the thread take-up lever to its highest position at the sewing start.
¡
Is the length of the upper thread trailing from the needle hole too
short?
Pull about 50 mm of thread through the needle hole at the sewing
start.
<B728>
¡
Is the trailing length of the upper thread too short after thread trim-
ming?
Adjust the thread guide.
¡
Are the threads not being trimmed cleanly?
Sharpen the fixed knives, or replace the fixed and movable knives if
necessary.
¡
Is the length of thread trailing out from the bobbin case after thread
trimming too short?
If the bobbin is spinning loosely, replace the bobbin tension spring
in the bobbin case.
¡
Is the needle up stop position too high?
Adjust the synchronizer.
¡
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 re-
place it.
¡
Is the presser foot pressure too strong?
Adjust the presser foot pressure.
¡
Is the angle of the feed dog incorrect?
Tilt the front of the feed dog up slightly.
¡
Is the needle and feed mechanism timing correct?
Retard the needle timing.
DB2-B727, B728
Possible cause
12. TROUBLESHOOTING
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