Husqvarna DM220 Workshop Manual page 21

ROTOR
Functional test
Preparations
Remove the screws on the right handle half to access the screws that hold the
electronics box above the speed sensor. Remove the box and refit the screws,
as these also hold the carbon brush holders.
Connect a measurement cable to each carbon brush and connect to the
measurement instrument. The carbon brushes need to be in good condition
to provide good contact with the collector.
Measuring cables
Use short measuring cables and lay these close to each other: the easiest way is
to twist them. Cables run in a coiled way give incorrect readings.
Inductance measurement – Henry (H)
Inductance measurement is applied to check the condition of the rotor. The
dimension is "Henry", abbreviated H (1H = 1000 mH). Resistance measure-
ment (ohm) produces no usable results.
Testing
Set the measuring instrument to measure mH. Turn the rotor shaft slowly with
a wrench on the speed sensor a few times so that measurements are obtained
for each winding on the rotor.
Measured values
Typical measured value for a complete rotor is around 12 mH. If any position
during the turn shows values below 9 mH, this is evidence of a defective
winding.
Bearing replacement
Press the rotor out of the gear
box cover.
Collector side – bearing
replacement
First remove the sensor.
Remove the bearing using a
puller.
Fit with a press force to the bea-
ring's inner ring.
Bearing replacement
Press the rotor out of the gear box cover
with a hydraulic press or standard puller
as shown in the illustration. Never knock
the rotor out of the gear box cover – this
will damage the worm gear.
Warning!
The hexagonal magnet in the middle of
the shaft is the sensor for motor's speed
control. Press force must not be applied
to the magnet.
Collector side – bearing replace-
ment
First remove the magnetic sensor in the
middle of the shaft. It has a screw thread.
Grip the rotor and remove the sensor.
Remove the bearing using a standard
puller.
You can assemble by pressing or knock-
ing the bearing in place. The press force
must be applied to the bearing's inner
ring.
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