Unicorn LS2-H550 - Page 40

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TROUBLESHOOTING GUIDE
Problem Cause Check Solution Page
Needle thread
slack.
Insufficient needle
thread tension
―
Increase needle thread
tension.
6
Excessive needle
thread tension
―
Decrease bobbin
thread tension.
6
Bobbin thr ead
slack.
Excessive needle
thread tension
―
Decrease needle
thread tension.
6
Insufficient needle
thread tension
―
Increase bobbin thread
tension.
6
Improper looping
stit ch tighten ing
Rough thread path Thread path
Polish with fine
san dp ap er.
Poor bobbin rotation
Tension of bobbin
thread leader
Replace bobbin, rotary
hook.
Rotary hook to rotary
hook stop gap too small
Gap
Adjust needle to rotary
hook timing.
15
Improper thread
cutt ing
a. Needle,
bobbin
threads not
cut
b. Nee dle
thread
not cut
c. Bobbin
thread
not cut
Movable knife, fixed
knife do not overlap.
― Adjust knives 19
Movable, fixed knife
edges worn or rough.
Knives Replace knives. 23
Movable knife does
not move
Thread cutter signal
tr ansmission
Check electrical
circuits; replace thread
cutter solenoid.
Improper needle
installation
Needle facing Reinstall needle. 4
Last stitch skipped,
needle thread not caught
by thread cutter.
Thread take-up
sprin g stroke
Adjust thread take-up
spring.
22
Movable knife, fixed
knife do not overlap
― Adjust knives. 19
Movable, fixed knives
dull.
Knives Replace knifes. 23
Movable knife, fixed
knife do not overlap
― Adjust knives. 19
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