Troubles And Corrective Measures - JUKI MO-6800S Series Engineer's Manual

8. Troubles and corrective measures

WARNING :
Turn OFF the power before starting the work so as to prevent accidents caused by abrupt start of the sewing machine.
Trouble
1. Needle thread breakage
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Cause (1)
1-1) Threading 1-A)
1-2) Thread path 2-A)
1-3) Needle guard 3-A)
1-4) Needle 4-A)
1-5) Needle heat 5-A)
1-6) Thread 6-A)
1-7) Thread tension 7-A)
1-8) Contact 8-A)
1-9) Double thread hook- 9-A)
ing (only for double
chainstitch)
Cause (2)
The thread is entangled with the thread
guide, or the machine head has been
incorrectly threaded.
Scratches, burrs or rust on the pawls or
needle holes of the throat plate, stitch
tongue, lower looper, double chain loop-
er, needle thread take-up, needle thread
presser spring, thread guide, or tension
discs causes friction.
The needle hits the needle guard in-
tensely, and sharp edges are produced
on them, causing thread breakage.
The needle is too thin for the thread.
The needle gets very hot, depending on
the type of materials, number of plies
and sewing speed, and causes the
thread to burn and break.
The thread is weak because of its poor
quality.
The thread tension is too high.
The double chain looper or lower looper
has been improperly positioned and
strikes the feed dog or throat plate.
Poor drawing up of the needle thread
causes the looper to catch it again.
Checking order and adjusting procedure
Refer to the threading diagram.
Remove such scratches, burrs, etc. and perform
thread path finishing. Replace major components
such as looper, which have been deformed, caus-
ing thread breakage.
Replace the needle and needle guard if they have
worn,
Replace the needle by a proper one.
Use a thinner needle. Reduce the sewing speed.
Use the needle cooler. Use an S-point needle or
needle for synthetic thread.
Replace the thread by one with good quality.
Reduce the thread tension. Check whether the
needle thread take-up guide and needle thread
guide are positioned too high, causing such ex-
cessive thread tension.
Properly position the double chain looper or lower
looper.
Increase the needle thread tension. Properly posi-
tion the thread cam. Properly position the double
chainstitch thread guide.