20 Husqvarna service manual 104 72 30-26
Step motor thread tension
The upper thread tension of the machine is automatically adjusted by a unipolar step motor
with 7.5 steps.
If the adjustment doesn’t work inspite of settings no 11 and no 12 being checked by means
of the service casette, the step motor or the thread tension device compl. should be replaced.
If the adjustment still doesn’t work the fault is in the circuit
board, its connections, or in some rare cases on the LCD board.
Step motor sewing head
The zigzag movement of the needle is done by a bipolar step motor with 7.5 steps.
If there is not any zigzag movement of the machine despite checking setting no 5 by means
of the service casette/program. Check the circuit board by means of gauge 412 02 56-01
(also check that the connections are undamaged).
If the zigzag movement still doesn’t work dismount the sewing head and check easy
running.
If this is allright try a new sewing head or step motor.
In some rare cases the fault can be in the LCD board.
The step motor of the guide (feeding)
The setting of the feeding direction from forward to backward between long and short
stitches is done by a bipolar step motor with 7.5 steps.
If this setting doesn’t work despite checking of setting no 21by means of the service casette.
Check the circuit board by means of gauge 412 02 56-01.
(Also check that the connections are undamaged).
If the adjustment still doesn’t work dismount the feeding guide compl. and check easy
running.
Is this alright try a new feeding guide or step motor.
In some rare cases the fault can be in the LCD board.
Step motor side feeding
The side feeding of the feed dog is created by a bipolar step motor with 7,5 steps.
If the side feeding of the feed dog does not work, check the pre-setting of the step motor,
the free-running of the feeding device and the sideways setting of the feed dog.
If the side feeding still does not work, check:
- the cable connection of the step motor to the circuitboard,
- the step motor,
- the smooth-running of the feeding movement,
- the circuit board,
- the LCD board.
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