
15
Operating instructions for eventual trouble shooting
Meaning of abbreviations:NP - Instruction manual
SK - Instructions for service
Note: When the machine is driven by a stop motor, it is indispensable to check up, before starting its repair, the setting of its
parameters according to NP, part B, par. 5.
Trouble
1. Upper thread breaking.
2. Lower thread breaking.
3. Skipped stitches at the seam begin-
ning after previous thread trimming.
Cause
1.1 Incorrect threading of the upper
thread.
1.2 Excessive thread tension.
1.3 Needle incorrectly inserted or da-
maged.
1.4 Needle thickness does not suit to
that of thread or sewn material.
1.5 Hook point sticks the thread.
1.6 Incorrect side setting of throat pla-
te post or needle bed shifting - lit-
tle gap between needle and pierc-
ing hole edge from hook side.
1.7 Rear needle guide in an excessive
back position - the right upper
thread is being slid on it.
1.8 Needle thread excessively elastic.
1.9 Low quality thread.
1.10 Needle thickness unsuitable for the
hole in the throat plate insert.
1.11 Damaged throat plate insert.
1.12 Incorrect setting of opening bob-
bin case lifter (little opening).
2.1 Incorrect threading.
2.2 Damaged bobbin.
3.1 Short thread end in needle after
trimming (thread too tensioned in
the moment of trimming).
3.2 Excessive thread tension.
3.3 Upper thread not squeezed, at the
first needle piercing, between
sewn material and edge of pierc-
ing hole.
Method of troubleshooting
Thread the upper thread according to NP,
par. 6.1.
Set the tension according to NP, par. 6.3.
Replace needle according to NP, par. 6.5.
Use a thicker needle.
Set distance between hook and needle
according to SK, par. 3.1.3 and 3.1.5.
Set according to SK, par. 3.3.2.
Correct distance between needle and
hook according to SK par. 3.1.3.
Set rear needle guide, so that its front
edge fits with the rear edge of the right
piercing hole.
Increase the hook timing and set the
needle bar height according to SK, par.
3.2.3.
Replace thread.
Replace insert according toNP, par. 4.1.6.
Replace insert.
Set according to SK, par. 3.1.6.
Thread according to NP, par. 6.2.
Replace bobbin.
Thread upper thread according to NP,
par. 6.1. Reduce tension of pretension
unit according to NP, par. 6.4. Accelerate
slightly OFF position of main tensioner
according to SK, par. 4.8; NP, part B , par.
5.2.2, 5.3.2; Mini-stop, par. 5.2.5 - pa-
rameter 192.
Set thread tension according to NP, par.
6.3.
Reduce height of feeder according to SK,
par. 3.6.3.2.1.
Put nearer top roller to needle and shift
it rearwards according to SK, par. 3.7.6.2.
Reduce rear guide, so that it touches
slightly sewn material with lowered top
roller.