JUKI DLN-6390 Engineer's Manual page 44

Troubles
6. Bobbin thread is not 6-1) Receding amount of moving
cut. (Needle thread
is cut.)
6-2) Position of bobbin thread is
6-3) A part of cutting blade
7. Thread trimming is 7-1) Amount of needle thread at
n o t c o m p l e t e d .
(Noise occurs from
the motor at the time
of thread trimming.)
7-2) There is no allowance of
7-3) Force of motor is not
7-4) Number of revolutions of
7-5) Thread tension No. 1 is
Cause (1)
knife is insufficient.
unstable.
section of knife is dull.
the time of thread trimming
is insufficient.
angle from thread trimming
to UP stop.
transmitted well.
thread trimming is low.
excessively tightened to
prevent rough motion of
needle thread.
Cause (2)
1)-A Needle thread only is
caught when moving
knife returns.
2)-A There is no groove for
guiding bobbin thread.
3)-A Cutting blade sections of
m o v i n g k n i f e a n d
counter knife are not
completely fit at the time
of thread trimming.
( I n s t a l l i n g a n g l e ,
position and inclination
of blade plane of counter
knife is not fit for the
blade section of moving
knife.)
1)-A Tension release timing
is too late.
1)-B Rising amount of disk at
the time of tension
release is small or the
disk is not rising.
2)-A Thread trimming timing
is too late.
2)-B Angle of UP stop is too
early.
3)-A Diameter of motor pulley
is too large.
3)-B Belt tension is low.
3)-C Inferior belt is used.
3)-D GAIN setting of control
box is improper.
4)-A Setting of number of
revolutions of thread
trimming of control box
is improper.
5)-A Oil amount in the hook is
small.
5)-B Height of needle bar is
improper and when it is
in the lower dead point,
needle thread is locked
and becomes resistance
since needle thread is
pinched with needle
hole and needle guard.
40
Corrective measures
Correct the receding amount of moving
knife according to 4-(4).
Check whether there is the groove for
guiding bobbin thread in the hook. If not,
replace the hook with one for thread
trimming.
Remove the throat plate, and move the
moving knife by hand. It is good that 3 pcs.
of cotton thread #50 are evenly cut when
3 pcs. of the thread are cut. If not, adjust
the position and sharpening procedure of
counter knife according to 4-(7) and 6-(1).
Check the set value of LS (Output start
angle of L output of G mode) according to
5.
Adjust the rising amount of disk according
to 4-(9).
Correct the thread trimmer cam timing
according to 4-(6).
Correct UP stop timing according to 4-(3).
Use the pulley (mark : 105) supplied as
accessories.
Correct the belt tension according to 4-(16).
Use the belt supplied as accessories.
Check the set value of GA (changeover of
high/low GAIN of A mode) according to 5.
Check the set value of T (setting of number
of revolutions of thread trimming of P
mode) according to the Instruction Manual.
Normally 200 rpm is set. However,
increase the number of revolutions of
thread trimming within the tolerance of
idling of bobbin at the time of thread
trimming.
After adjusting oil amount in the hook
according to the Instruction Manual,
decrease the tension of thread tension
No. 1 within the range where thread
does not move roughly between thread
tensions No. 1 and No. 2.
After adjusting the height of needle bar
according to 4-(21), decrease the tension
of thread tension No. 1 within the range
where thread does not move roughly
between thread tensions No. 1 and No. 2.