13. TROUBLESHOOTING
/
Problem
Possible
cause
Page
4.
Skipped stitches at sewing • Are the thread take-up spring tensions
too
strong?
start
Reduce the tension
of
the thread take-up springs.
41
•
Is
the thread tension spring operating range too large?
Lower the position
of
the thread tension spring.
40
/::::--_
•
Is
the needle too wide?
Try using a needle
with
a
count
that is one
lower
than the current
..............
needle.
-
.......
<8721/8723>
•
Is
the thread take-up lever at its highest position at the sewing start?
Set the thread take-up lever to its highest position at the sewing start.
26
Thread unravelling at
•
Is
the length
of
the upper thread trailing
from
the needle hole
too
sewing start
short?
Pull about
50
mm
of
thread through the needle hole
at
the sewing
start.
26
'~Upper
<8722/8724>
; - thread
•
Is
the trailing length
of
the upper thread too short after thread
trim-
11
,,
ming?
•
Adjust the pretension.
32
\j
• Are the threads not being
trimmed
cleanly?
Sharpen the fixed knives,
or
replace the fixed and movable knives
if
necessary.
54
•
Is
the length
of
thread trailing out from the bobbin case after thread
trimming
too short?
If the bobbin is spinning loosely, replace the bobbin tension spring
in the bobbin case.
22
If using woolly nylon thread
as
the lower thread, the amount
of
lower
thread
trailing from the bobbin case
will
be
shorter than normal,
so
replace the movable knives
with
movable knives 5 (159915-001).
55
•
Is
the needle up stop position
too
high?
Adjust the synchronizer.
52
5.
Uneven seam
•
Is
the presser
foot
pressure
too
weak?
Adjust the presser
foot
pressure.
32
~
•
Is
the feed dog
too
low?
Adjust the feed dog height.
44
•
Is
the bobbin scratched?
...
....._
.............
If the bobbin is damaged, smooth
it
with
an
oiled grindstone
or
re-
place it.
-
'
./
57
082-8720 series
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