Common Traction System Difficulties - JLG 1930ES Service Maintenance Manual

Common Traction System Difficulties

1. Short-Circuit Motor Armature
This issue will allow the vehicle to drive very slowly
or not at all. Rapid motor overheating (one motor)
will result.
This situation can be detected by elevating the vehi-
cle's front wheels and engaging drive (platform
stowed). Under DIAGNOSTICS - TRACTION, the
JLG Analyzer's ARM CUR display (Armature Current
Reading) will exceed 120A. The FLD CUR display
(Field Current Reading) will hover around 40A. Nei-
ther wheel will rotate at normal speed, but it will be
possible to rotate the drive wheel by hand. The
Power Module's self-diagnostics cannot detect this
fault since the situation appears identical to climbing
a steep grade.
To find the source of the difficulty, pull the Main Bat-
tery Disconnect and disconnect the Armature Wiring
(heavy red and black conductors) from the sus-
pected drive motor leading to the Power Module's
M1 and M2 Terminals. Re-test the traction function.
If the remaining drive motor is able to reach full
speed (and Armature Current is less than 50A), the
drive motor that has been disconnected is fault.
Investigate for crushed and burned cables. Note if
the drive motor smells burned.
2. Short-Circuit Brake Release
This issue will not allow the vehicle to drive. Rapid
motor overheating (both motors) will result. Contin-
ued attempts to drive the vehicle may result in arma-
ture damage.
This situation can be detected by elevating the vehi-
cle's front wheels and engaging drive (platform
stowed). Under DIAGNOSTICS - TRACTION, the
JLG Analyzer's ARM CUR display (Armature Current
Reading) will exceed 120A. The FLD CUR display
(Field Current Reading) will hover around 40A. Nei-
ther wheel will rotate, and it will be impossible to
rotate either drive wheel by hand. The Ground Mod-
ule cannot detect this fault during power-up or self-
test since energizing the brakes could pose a haz-
ard. However, it may detect this issue during Drive
(investigate using JLG Analyzer).
To find the source of the difficulty, remove the rear
cover from either drive motor. Insert voltmeter leads
into the white connector leading to the brake sole-
noid (yellow and brown wires) and attempt to drive
(Platform Mode). The Ground Module will apply
approximately 24V to the brake release solenoids
(wired in parallel) during drive, but will reduce this
voltage in the event of a short-circuit. If this voltage is
improper (less than 8V), investigate using resistance
measurement (refer to Drive Motor Electrical Evalua-
3121166
SECTION 3 - CHASSIS & SCISSOR ARMS
tion). Suspect damaged cabling, burned cabling, or
faulty brake release solenoids. Trace the brake
release cabling from the Power Module Compart-
ment to the Ground Module Connector J1-24.
3. Open-Circuit Brake Release
This issue will not allow the vehicle to drive. Rapid
motor overheating (both motors) will result. Contin-
ued attempts to drive the vehicle may result in arma-
ture damage.
This situation can be detected by elevating the vehi-
cle's front wheels and engaging drive (platform
stowed). Under DIAGNOSTICS - TRACTION, the
JLG Analyzer's ARM CUR display (Armature Current
Reading) will exceed 120A. The FLD CUR display
(Field Current Reading) will hover around 40A. It is
possible that one wheel may rotate, or neither may
rotate (depending on the location of the open-cir-
cuit). Listen for the brake release solenoid when acti-
vating drive. The Ground Module cannot detect this
fault during power-up or self-test since energizing
the brakes could pose a hazard. However, it may
detect this issue during Drive (investigate using JLG
Analyzer).
If one wheel rotates, the open-circuit is located in the
wiring for that specific drive motor (Power Module
compartment or Drive Motor Cable). Investigate for
improper crimps, unlatched connectors, damaged
cables, or open brake release solenoids (refer to
Drive Motor Electrical Evaluation).
If neither wheel rotates, the open-circuit is located in
the wiring between the Power Module compartment
and Ground Module. Using a voltmeter, measure the
brake release voltage on either brake connector in
the Power Module compartment during drive
(should be approximately 24V). Investigate for
improper crimps, unlatched connectors, damaged
harnessing, or a faulty Ground Module. As an alter-
native, insert a short piece of wire with a Deutsch
Female Crimp directly into Ground Module's J1-24
and measure voltage as a diagnostic measure (eject
vehicle harness from that pin).
– JLG Lift – 3-37