JUKI LK-1900AN Engineer's Manual page 112

Trouble
4. Thread breakage
To the next page
Cause (1)
4-1) Scratches on the inner
hook
4-2) Thread enters into the
shuttle.
4-3) Scratches on the shuttle
driver.
Cause (2)
1-A) Scratches on section A (Con-
tact of the inner hook with the
needle)
1-B) Scratches on section B
((Scratches occur when the
needle is bent or broken.)
1-C) Scratches on section C (Needle
scratches the inner hook when
removing the inner hook.)
1-D) Scratches on section D
2-A) Position of the shuttle upper
spring is wrong.
2-B) Blade point section A of the
shuttle is round.
2-C) Position of the shuttle is wrong.
2-D) Needle thread tension is too low.
2-E) Thread take-up spring tension is
too low.
2-F) Length of the remaining needle
thread is too long.
2-G) The specified inner hook and
shuttle driver are not used.
Check and corrective measures
After polishing the blade point of the inner
hook with oilstone, polish it with polish-
ing powder. Properly adjust the clearance
between the needle and the inner hook.
After polishing the blade point of the inner
hook, polish it with polishing powder.
After polishing the blade point of the inner
hook, polish it with polishing powder.
After polishing the blade point of the inner
hook, polish it with polishing powder.
Properly adjust the position of the shuttle
upper spring.
Replace the inner hook.
Properly adjust the position of the shuttle.
Properly adjust the needle thread tension.
Adjust the thread take-up spring.
Properly adjust the thread tension No. 1
asm.
Use the specified parts.
Remove the scratches and polish with buff,
or replace the shuttle driver.