Unicorn DB2-H515 - Page 39

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Problem Cause Check Solution Page
Needle thread
slack.
Insufficient needle
thread tension
―
Increase needle thread
tension.
12
Excessive needle
thread tension
―
Decrease bobbin
thread tension.
12
Bobbin thread
slack.
Excessive needle
thread tension
―
Decrease needle
thread tension.
12
Insufficient needle
thread tension
―
Increase bobbin thread
tension.
12
Improper looping
stitch tightening
Rough thread path Thread path
Polish with fine
sandpaper.
Poor bobbin rotation
Tension of bobbin
thread leader
Replace bobbin, rotary
hook.
Rotary hook to rotary
hook stop gap too small
Gap
Adjusting the rotary hook
timing.
20
Improper thread
cutting
a. Needle, bobbin
threads not cut
b. Needle thread
not cut
c. Bobbin thread
not cut
Movable knife, fixed
knife do not overlap.
― Adjust knives
Movable, fixed knife
edges worn or rough.
Knives Replace knives.
Movable knife does
not move
Thread cutter signal
transmission
Check electrical
circuits; replace thread
cutter solenoid.
Improper needle
installation
Needle facing Reinstall needle. 7
Last stitch skipped,
needle thread not caught
by thread cutter.
Thread take-up
spring stroke
Adjust thread take-up
spring.
Movable knife, fixed
knife do not overlap
― Adjust knives. 15
Movable, fixed knives
dull.
Knives Replace knives. 15
Movable knife, fixed
knife do not overlap
― Adjust knives. 15
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