JLG M450 Service Manual - Manual (Page 211)

SECTION 7 - BASIC TROUBLESHOOTING, ELECTRICAL INFORMATION, & SCHEMATICS
3121829 – JLG Lift – 7-1
SECTION 7. BASIC TROUBLESHOOTING, ELECTRICAL INFORMATION, & SCHEMATICS
7.1 GENERAL
This section contains basic troubleshooting information
and basic electrical information to be used for locating
and correcting most of the operating problems which may
develop. If a problem should develop which is not pre-
sented in this section or which is not corrected by listed
corrective actions, technically qualified guidance should
be obtained before proceeding with any maintenance.
7.2 TROUBLESHOOTING
The troubleshooting procedures applicable to the aerial
platform are listed and defined in Table 7-1 through Table
7-6. As an aid to table use, the aerial platform is divided
into four major groups, each covered separately within
this section. These groups are as follows: elevation sys-
tem, chassis assembly, hydraulic system and electrical
system.
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
that 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 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.
The reference for improper function of a hydraulic system,
where the cause is not immediately apparent, should be
the Troubleshooting Chart. 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 system-
atic check of the circuit components, beginning with the
control, would follow. For aid in troubleshooting, refer to
the Illustrated Parts Manual for hydraulic diagrams of the
various circuits