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Publicidad
Problem
4. Skipped stitches at sewing
start
Thread unravelling at
sewing start
Upper
thread
5. Uneven seam
6. Material slippage
¡
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.
<7270>
¡
Is the thread take-up lever at its highest position at the sewing start?
0749M
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.
<7280>
¡
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.
0623M
¡
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.
0473M
¡
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.
0750M
Possible cause
SB-7270, 7280
12. TROUBLESHOOTING
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