Pump Motor Electrical Evaluation - JLG 1930ES Service Maintenance Manual

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 Figure 7-2., Resistance Measurement. Make all
measurements with a voltmeter set to resistance scale
(Ohms). Disconnect the Main Battery Disconnect and all
pump motor cables during this analysis.
• Resistance < 5 Ohms between Motor Termninals.
The internal windings are very low impedance and
should appear to be a short-circuit for an ordinary volt-
meter (other tests can determine if the windings are
truly shorted). High resistance can signal worn
brushes, a faulty commutator, or open windings.
• Resistance > 1 MegaOhms between Motor Termi-
nals and Motor Housing. The internal windings
should be electrically isolated from the motor housing.
Low resistance may be an indication of a broken motor
terminal, damaged brush, faulty commutator, or
burned winding.
Common Difficulties
The following difficulties can be examined using the JLG
Analyzer, a voltmeter, and simple hand tools. Unless oth-
erwise 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 firm, level surface for
all analysis.
1. Open-Circuit between +B 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 DIAGNOSTICS -
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, exam-
ine the cable between the terminal and the Power
Module compartment. Inspect crimps for corrosion
and ensure that bolted connections are tight.
Ensure that the cable is not crushed where it passes
between the frame side sheets and the cylinder
assembly.
3121166
2. Open-Circuit between Pump Motor Negative Ter-
minal and P 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 DIAGNOSTICS -
PUMP , the JLG Analyzer will show PUMP PWM 100%
and PUMP CUR 0.0A when Lift Up is operated from
Ground Mode.
After ensuring there is not an Open-Circuit between
the +B Terminal and Pump Motor Positive Terminal,
check that the voltage measured between the Pump
Motor Negative Terminal and Ground Reference is
24V. If not, examine the issues within Open-Circuit
Pump Motor. This voltage should ramp to approxi-
mately 0V when Lift Up is operated from Ground
Mode. If not, examine the cable between the termi-
nal and the Power Module compartment (P Termi-
nal). Inspect crimps for corrosion and ensure that
bolted connections are tight. Ensure that the cable is
not crushed where it passes between the frame side
sheets and the cylinder assembly.
3. Open-Circuit Pump Motor
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 DIAGNOSTICS -
PUMP , the JLG Analyzer will show PUMP PWM 100%
and PUMP CUR 0.0A when Lift Up is operated from
Ground Mode.
Pull the Main Battery Disconnect to completely de-
energize the Control System. Next, detach the cable
from Pump Motor Positive Terminal. Using a voltme-
ter set for resistance measurement (Ohms), ensure
that the resistance between the Pump Motor Positive
and Negative Terminals is less than 2 Ohms. If not,
examine the pump motor for worn brushes or bro-
ken terminals. After examination, re-connect the
Pump Motor Positive Terminal and the Main Battery
Disconnect.
4. Short-Circuit between Pump Motor Positive and
Negative Terminals
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 DIAGNOSTICS -
PUMP , the JLG Analyzer will show an erratic reading
for PUMP PWM % and PUMP CUR will hover around
150A when Lift Up is operated from Ground Mode.
Pull the Main Battery Disconnect to completely de-
energize the Control System. Next, detach both
Pump Motor Terminals and insulate them indepen-
dently. Re-connect the Main Battery Disconnect and
re-try Lift Up. If the same symptoms persist (erratic
PUMP PWM%, PUMP CUR around 150A), examine
the cabling between the Pump Motor and Power
– JLG Lift –
SECTION 4 - HYDRAULICS
4-7