Generac Power Systems 941-2 Service Manual page 69

GENERAL
The AC generator's output voltage is controlled by a
"computerized" speed control system. This system
changes engine speed in response to changes in the
AC output voltage at varying engine loads. The speed
control system consists of (a) the A6060 circuit board
and (b) a stepper motor.
A6060 CIRCUIT BOARD
This circuit board utilizes a closed-loop, proportional-
derivative controller circuit which regulates the gener-
ator's RMS voltage by changing engine speed. The
system attempts to maintain an output voltage of
about 115 volts at the lowest rpm and 120 volts up to
the maximum rpm.
The A6060 circuit board controls a stepper motor by
calculating the number of steps the motor needs to
take and then supplying the necessary signals to the
motor to take those steps.
STEPPER MOTOR PROBLEMS
INTRODUCTION:
Some stepper motor problems that might occur
include the following:
• Throttle linkage or carburetor throttle shaft sticking,
or linkage disconnected.
• Stepper motor failed or seized.
• Electrical connections to stepper motor broken or
disconnected.
• Electrical leads to stepper motor are connected
wrong.
THROTTLE LINKAGE:
Check throttle linkage and carburetor throttle shaft for
binding, disconnected linkage. This type of problem
will usually result in the carburetor throttle lever not
moving. If the throttle lever does not move, the throttle
may be stuck at a permanently open throttle or a per-
manently closed throttle as follows:
1. If the throttle is open, engine will start but will accelerate quick-
ly and uncontrollably. It will shut down when speed exceeds
about 4200 rpm.
2. If the throttle is closed, engine will not accelerate under load.
STEPPER MOTOR FAILED OR SEIZED:
The engine will start but stepper motor will not turn. If
an open throttle condition exists, either of the follow-
ing might occur:
1. Engine may accelerate and shut down at 4200 rpm.
2. Engine may shut down after 15 seconds due to an overvoltage
condition.
If throttle is closed, engine will be unable to acceler-
ate under load and AC output will be low.
A failed stepper motor may also turn erratically. If this
is the case, engine speed and AC output voltage will
be erratic under constant load.
Figure 1. Speed Control System
Section 3.6
SPEED CONTROL SYSTEM
Page 3.6-1