Generac Power Systems 941-2 Service Manual page 70

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.
Page 3.6-2
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