Brother DB2-B771A Instruction Manual page 81

Problem
4. Skipped stitches at sewing
start
Thread unravelling at sew-
ing start
Upper
thread
5. Uneven seam
6. Large degree of puckering
(excess tension)
¡ Is the thread tension spring tension too strong?
Reduce the tension of the thread tension spring.
¡ 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.
<B771A>
¡ 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.
<B772A>
¡ Is the trailing length of the upper thread too short after thread trim-
ming?
Adjust the pretension.
¡ 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 anti-spin 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 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.
¡ Is the thread tension spring tension too strong?
Make the thread tension 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 position
as possible.
¡ Is the presser foot pressure too strong?
Adjust the presser foot pressure.
¡ Is the sewing speed too fast?
Reduce the sewing speed slightly.
¡ Is the angle of the feed dog incorrect?
Tilt the front of the feed dog down slightly.
0978M
Possible cause
DB2-B771A, B772A
15. TROUBLESHOOTING
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