JUKI MO-6800S Series Engineer's Manual page 64

WARNING :
Turn OFF the power before starting the work so as to prevent accidents caused by abrupt start of the sewing machine.
Trouble
11. Overlocking chain-off thread is
bad. (Provided that no chain-
off trouble occurred when sew-
ing operation was done with
materials set on the machine.)
12. Problems with double chain-
stitch chain-off thread
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Cause (1)
11-1) Position of the throat 1-A)
plate
11-2) Feed dog 2-A)
2-B)
11-3) Adjustment of looper 3-A)
11-4) Thread tension 4-A)
4-B)
12-1) Adjustment of loop- 1-A)
ers
12-2) Needle Guard 2-A)
12-3) Position of the throat 3-A)
plate
3-B)
Cause (2)
The throat plate has been improperly
positioned longitudinally, and chain-off
thread gets in between the main feed
dog and throat plate, causing defective
chain-off thread.
The auxiliary feed dog is too high, and
interferes with chain-off thread. The
auxiliary feed dog is too low. (Lower than
the main feed dog by more than 0.5 mm)
The auxiliary feed dog has scratch.
Adjustment of loopers for producing
chain-off thread without materials re-
quires higher accuracy.
The thread tension is too low.
The needle thread tension is too high,
causing damaged balance with other
thread tension.
Adjustment of the loopers for produc-
ing chain-off thread without materials
requires higher accuracy.
The needle guard is too high, damaging
loops.
The needle comes into contact with
the front edge of the needle hole in the
throat plate.
The lateral position of the throat plate
with respect to the feed dogs is wrong,
causing chain-off to drop in.
Checking order and adjusting procedure
Correctly position the throat plate.
Refer to the pertinent Standard Adjustment.
Repair or replace the auxiliary feed dog.
Refer to the pertinent Standard Adjustment.
Slightly increase the tension.
Check whether the needle thread take-up guide
or needle thread guide is positioned too high with
consequent excessive needle thread tension. And
if so, correct it.
Refer to the pertinent Standard Adjustment.
Refer to the pertinent Standard Adjustment.
Correctly position the throat plate.