JUKI LK-1900B series, Engineer'S Manual, Page: 74 / 174

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(42) Bobbin case with an idling prevention spring
WARNING :
Turn OFF the power before starting the work so as to prevent accidents caused by abrupt start of the
sewing machine.
The LK-1900B Series use bobbin cases with an idling prevention springs.
Adjust the tension of the an idling prevention spring as follows:
If the bobbin races Increase the spring tension.
If loose stitches result Decrease the spring tension.
1) How to adjust the tension of the an idling prevention spring
1. Remove the spring as illustrated below, using an old sewing machine needle. (At this time, hold the
spring with your thumb to prevent it from jumping out.)
2. Adjust the spring pressure by changing the height of the arch of the spring.
3. Set ear
❶ first, and insert the sewing machine needle to push the central part of the spring, then set ear
❷ .
1. 2. 3.
0.3mm ± 0.2mm
Change this
height
Ears
2) When using a bobbin case
1. When using a bobbin case with an idling prevention spring, be sure to orient the bobbin as shown be-
low:
Rotation of bobbin