SECTION 4 - BASIC HYDRAULIC INFORMATION & SCHEMATICS
4-2
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4.3
PUMP/MOTOR
Theory of Operation
The Power Module is essentially a "low-side" switch for the
pump motor. The positive terminal of the pump is tied to
Battery Positive after the Line Contactor. The negative ter-
minal of the pump connects to the P Terminal of the
Power Module, which switches current through MOSFET
transistors to the Battery Negative.
For variable speed pump operation, the MOSFET transis-
tors switch On and Off at high frequencies (16kHz). The
Duty Cycle is varied to control the voltage applied to the
pump motor. When the MOSFET's spend 50% of the
period On and 50% Off, approximately ½ of the available
Battery Voltage will be applied to the pump motor. Simi-
larly, the MOSFET are On continuously (100% Duty Cycle)
to apply all available Battery Voltage to the pump motor
(as in Lift Up at full speed).
When the Control System is energized, the voltage at the P
Terminal will be approxi24V (referenced to -B)
when the pump is static. The P Terminal will be approxi-
mately at +1V (referenced to -B) when the pump is run-
ning at full speed (Lift Up from Ground Mode).
Pump Motor Electrical Evaluation
Several basic electrical tests can be performed on the
Pump Motor. Failure of one of these evaluations is signifi-
cant and may indicate that the device is physically dam-
aged.
Refer to Section 8. Make all measurements with a voltme-
ter set to resistance scale (Ohms). Disconnect main power
at the batteries and all pump motor cables during this
analysis.
• Resistance < 5 Ohms between Motor Terminals.
The internal windings are very low impedance and
should appear to be a short-circuit for an ordinary
voltmeter (other tests can determine if the windings
are truly shorted). High resistance can signal worn
brushes, a faulty commutator, or open windings.
• Resistance > 1 Mega-Ohms between Motor Termi-
nals and Motor Housing.
The internal windings
should be electrically isolated from the motor hous-
ing. Low resistance may be an indication of a broken
motor terminal, damaged brush, faulty commutator,
or burned winding.
Troubleshooting
The following difficulties can be examined using the JLG
Analyzer, a voltmeter, and simple hand tools. Unless other-
wise noted, the Control System shall be energized in
Ground Mode during testing. For a convenient Ground
Reference, place the black meter lead on the negative post
of the left battery in the left-side batter compartment. The
vehicle should be placed on a smooth, firm, and level sur-
face for all analysis.
1. Open-Circuit bB Terminal and Pump
Motor Positive Terminal
This issue will allow the vehicle to drive, but Lift
Up and Steer Functionality will be lost and the
Pump Motor will not operate. Under DIAGNOS-
TICS - PUMP, the JLG Analyzer will show PUMP
PWM 100% and PUMP CUR 0.0A when Lift Up is
operated from Ground Mode.
As shown in the diagram, the voltage measured
between the Pump Motor Positive Terminal and
Ground Reference should be 24V. If it is not,
examine the cable between the terminal and the
Power Module compartment. Examine crimps
for corrosion and ensure that bolted connec-
tions are tight. Ensure that the cable is not
crushed where it passes between the frame side
sheets and the cylinder assembly.
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