JLG 19AMI (3120758) Service Manual - Manual (Page 49)

SECTION 3 - TROUBLESHOOTING
3120758 – JLG Lift – 3-1
SECTION 3. TROUBLESHOOTING
3.1 GENERAL
This section contains troubleshooting information to be
used for locating and correcting most of the operating
problems which may develop in the aerial platform. If a
problem should develop which is not presented in this
section or which is not corrected by listed corrective
actions, technically qualified guidance should be obtained
before proceeding with any maintenance.
3.2 TROUBLESHOOTING INFORMATION
The troubleshooting procedures applicable to the aerial
platform are listed and defined in Table 3-1, AC Unit Trou-
bleshooting and Table 3-2, DC Unit Troubleshooting.
Each malfunction within an individual group or system is
followed by a listing of probable causes which will enable
determination of the applicable remedial action. The prob-
able causes and the remedial action should, where possi-
ble, be checked in the order listed in the tables.
It should be noted that there is no substitute for a thor-
ough knowledge of the equipment and related systems.
It should be recognized that the majority of the problems
arising in the machine will be centered in the hydraulic
and electrical systems. For this reason, every effort has
been made to ensure that all likely problems in these
areas are given the fullest possible treatment. In the
remaining machine groups, only those problems which
are symptomatic of greater problems which have more
than one probable cause and remedy are included. This
means that problems for which the probable cause and
remedy may be immediately obvious are not listed in this
section.
The first rule for troubleshooting any circuit that is hydrau-
lically operated and electrically controlled is to determine
if the circuit is lacking hydraulic oil and electrical control
power. This can be ascertained by overriding the bypass
valve (mechanically or electrically) so that oil is available
to the function valve, then overriding the function valve
mechanically. If the function performs satisfactorily, the
problem exists with the control circuit.
3.3 HYDRAULIC CIRCUIT CHECKS
The first reference for improper function of a hydraulic sys-
tem, where the cause is not immediately apparent, should
be the Hydraulic Diagram Circuit. The best place to begin
the problem analysis is at the power source (pump). Once
it is determined that the pump is serviceable, then a sys-
tematic check of the circuit components, would follow.
NOTE: For aid in troubleshooting, refer to Figure 3-5. for
HYDRAULIC DIAGRAM circuit.
3.4 ELECTRICAL SYSTEM - MULTIMETER
BASICS
A wide variety of multimeters or Volt Ohm Meters (VOM)
can be used for troubleshooting your equipment. A digital
meter with reasonable accuracy (within 7%) is recom-
mended for the measurements in these procedures. This
section shows diagrams of a common, digital VOM con-
figured for several different circuit measurements. Instruc-
tions for your VOM may vary. Please consult the meter
operator’s manual for more information.
Grounding
"Grounding the meter" means to take the black lead
(which is connected to the COM (common) or negative
port) and touch it to a good path to the negative side of
the voltage source.
Backprobing
To "backprobe" means to take the measurement by
accessing a connector’s contact on the same side as the
wires, the back of the connector. Readings can be done
while maintaining circuit continuity this way. If the connec-
tor is the sealed type, great care must be taken to avoid
damaging the seal around the wire. It is best to use
probes or probe tips specifically designed for this tech-
nique, especially on sealed connectors. Whenever possi-
ble insert probes into the side of the connector such that
the test also checks both terminals of the connection. It is
possible to inspect a connection within a closed connec-
tor by backprobing both sides of a connector terminal and
measuring resistance. Do this after giving each wire a
gentle pull to ensure the wires are still attached to the con-
tact and contacts are seated in the connector.
Min/Max
Use of the "Min/Max" recording feature of some meters
can help when taking measurements of intermittent condi-
tions while alone. For example, you can read the voltage
applied to a solenoid when it is only operational while a
switch, far from the solenoid and meter, is held down.