Test 5 - Check Stepper Motor Control - Generac Power Systems GP Series Diagnostic And Repair Manual

Section 4 AC Diagnostic Tests
Table 4-1. Test 4 Results – Fixed Excitation Test/Rotor Amp Draw Test (8-20 kW)
Results:
Voltage Results Wire 2 & 6
Excitation Winding
Voltage Results Wire 11S & 44S
Voltage Results Wire 11S & 44S
Rotor Amp Draw 12.5 kW
Rotor Amp Draw 15 kW
Rotor Amp Draw 17.5 kW
Test 5 – Check Stepper Motor Control
Procedure
Remove air cleaner cover to access stepper motor.
1.
Move throttle by hand and verify stepper motor,
2.
linkage and throttle do not bind in any way. If any
binding is felt, repair or replace components as
needed. Some resistance should be felt as the
stepper motor is moved.
A
A. Stepper Motor B. Linkage
Figure 4-9. Stepper Motor, Linkage and Throttle
A
A. Full Throttle
B. Closed Throttle
Figure 4-10. Throttle Positions
Move the throttle to the closed position by pushing
3.
the throttle down as looking from above.
38
A B
Above 60 Above 60 Below 60
VAC VAC
Above 50 Below 50 Above 50
VAC VAC
Above 50 Below 50 Above 50
VAC VAC
1.76-2.05 1.76-2.05 1.76-2.05
1.76-2.05 1.76-2.05 1.76-2.05
1.76-2.05 1.76-2.05 1.76-2.05


Match results with letter and refer to flow chart "Problem 2"
B
C
004657
C. Throttle
B
004640
C D
Zero or Residual Volts
VAC
Zero or Residual Volts
VAC
Zero or Residual Volts
VAC
Zero Current Draw
Zero Current Draw
Zero Current Draw
a. Set the idle control switch to OFF.
b. Set the start-run-stop switch (SW1) to START.
c. Watch for stepper motor movement. It should
move to the wide open position during
cranking. Once the unit starts the stepper
motor should move the throttle to a position to
maintain 60 Hertz.
If no movement is seen in step 3 remove the
4.
control panel cover.
a. Verify the six pin connector on the printed
circuit board is seated properly. Remove the
connector and then replace it and test again.
b. See Figure
correctly.
See Figure
5.
pin connector from printed circuit board.
Set DMM to measure resistance (ohms).
6.
Carefully measure from the end of the six pin
7.
harness as follows:
NOTE: Press down with the meter leads on the exposed
connector terminals. Do not probe into the connector.
A. Black
B. Brown
C. Yellow
Figure 4-11. Six Pin Connector Wire Colors
E F
Below 60 Below 60
VAC VAC
Below 50 Below 50
VAC VAC
Below 50 Below 50
VAC VAC
Above 2.5A 1.76-2.05
Above 2.5A 1.76-2.05
Above 2.5A 1.76-2.05

2-1. Verify the switches are set
4-11. If problem continues remove six
A
B
C
D
E
F
D. Orange
E. Red
F. Empty
Diagnostic Repair Manual
G
Above 60 VAC
Above 50 VAC
Above 50 VAC
Zero Current
Draw
Zero Current
Draw
Zero Current
Draw
004641