Generac Power Systems 940-2, 941-2 Testing The Stepper Motor, Section SPEED CONTROL SYSTEM

Section 3.6

SPEED CONTROL SYSTEM

ELECTRICAL CONNECTIONS BROKEN:

If one or more of the electrical connections to the stepper motor are broken or disconnected, either of the following might occur:

1.The stepper motor may not turn at all.

2.The stepper motor may turn erratically.

If the stepper motor does not turn, symptoms will be the same as for a failed or seized stepper motor.

LEADS CONNECTED WRONG:

Incorrectly connected electrical leads to the stepper motor can result in any one of the following:

1.Stepper motor may not turn at all.

2.Stepper motor may turn erratically.

3.Stepper motor may turn backwards.

If the stepper motor does not turn, engine will start and the following may occur:

1.If throttle is open, engine will accelerate and shut down when speed reaches 4200 rpm or after 15 seconds due to overvolt- age condition.

2.If throttle is closed, engine will be unable to accelerate under load.

If the stepper motor turns erratically, engine speed and AC output voltage will be erratic under a constant load. The AC output will not terminate.

If the stepper motor is turning backwards, engine will accelerate and shut down at 4200 rpm.

TESTING THE STEPPER MOTOR

GENERAL:

The Stepper Motor consists of an electric motor plus a small gearbox. It is shown pictorially and schemati- cally in Figure 3. The four (4) motor windings can be tested for (a) continuity and (b) shorts to the case.

It is difficult to perform an operational test of the motor since the amount of motor arm movement is so small.

TESTING FOR OPEN CONDITION:

To test the motor windings for an open circuit condi- tion, proceed as follows:

1.Unplug the Stepper Motor connector from its receptacle on the A6060 circuit board.

2.Set a volt-ohm-milliammeter (VOM) to its "Rx1" scale and zero the meter.

3.Connect one VOM test probe to the connector pin to which the RED wire attaches. This is the +DC side of all windings. Then, connect the other VOM test probe as follows:

a. To the ORANGE wire connector pin.

Approximately 19-21 ohms should be indicated.

b. To the YELLOW wire connector pin. About 19- 21 ohms should be read.

c. To the BROWN wire pin for a reading of 19-21 ohms.

d. To the BLACK wire connector pin for a reading of about 19-21 ohms.

TESTING FOR SHORTED CONDITION:

1.Set the VOM to its "Rx10,000" or "Rx1 K" scale and zero the meter.

2.Connect one VOM test probe to the RED wire connector pin, the other test probe to the Stepper Motor case. The meter should read infinity". Any reading other than "infinity" indicates a shorted winding.

Replace the Stepper Motor if it fails any part of the test.

Figure 2. The Stepper Motor Connector

Figure 3. The Stepper Motor

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