Husqvarna K7000 Ring Workshop Manual

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32TROUBLESHOOTING15MotorDismantle the cutting machine so that the motor's connectors areaccessible. The motor does not need to be removed from themachine.Short-circuit testingCheck first to make sure that the motor does not have shortedwindings to earth (motor material). This is easy to do using amultimeter on the contact X1. Set the multimeter in position forconnection testing with a buzzer. A shorted motor gives a closedcircuit between the earth cable (4) and one of the phases (1, 2, 3).If no fault is indicated, the test must be extended to includeinsulation testing as indicated below.Resistance and induction measurementThe following test shows whether the motor has shorted windingturns. A small number of shorted winding turns means that themotor loses power but can work for a short time. Fully shortedwindings mean that the motor will not start.The check is carried out with resistance measurement in Ω(Ohm), and inductance measurement in mH (milliHenry). Anintact motor gives values of approx. 2 Ohm or 10–12 mH.Measure between 1–2, 2–3 and 3–1. If the deviation is more than20 % lower, the motor must be regarded as defective.Note: Measurement instruments may give incorrect readings.Therefore, place greater emphasis on the relative values between thewindings than on the absolute readings.Insulation testingThe insulation test is a test which indicates where there is inade-quate insulation between the motor's windings and earthing.Insulation measurement takes place in the same way as theinitial check between the earth cable (4) and phases 1, 2 and 3.The insulation tester is set for a 1,000-volt voltage. The test mustshow maximum resistance for the result to be approved.Rotor magnetsThe rotor in the motor has permanent magnets with high magneticenergy, known as neodymium magnets. As with all permanentmagnets, high temperature, blows, vibration and powerful externalfields “wear out” the magnetic force. The service life of the machineis probably not limited by the rotor. A defective rotor will reducemotor output.Neodymium is an earth metal, and the magnetic strength variesslightly from magnet to magnet at the time of manufacture. It istherefore impossible to set a precise limit as to when the rotor isconsidered to be consumed. If the phase voltage in the test belowexceeds 65 volts, the rotor must be considered usable.The rotor magnets are tested as follows:Remove the belt pulley from the motor and replace the screw witha long screw from which the head has been cut off. Connect ascrewdriver to the screw.Connect test cables between two phases and set the multimeterto read alternating current. Rotate the motor to 1,000 revolutionsper minute, and check this with a tachometer. The typical normalvalue is 73 volts at 1,000 revolutions per minute.Repeat the test for all three phases: these must all give the samevalue, otherwise there is a fault in the stator windings.X1X21X12 3 41X12 3 4Short-circuit testingMeasure between 1–4, 2–4 and 3–4Testing stator windingsMeasure between 1–2, 2–3 and 3–1Resistance measurement approx. 2 OhmInductance measurement approx. 10–12 mHInsulation testingMeasure between 1–4, 2–4 and 3–4Rotor testingMeasure between 1–2, 2–3 and 3–1Normal value: 73 volts rms at 1,000 rpmMinimum value: 65 volts rms at 1,000 rpm