JLG 120HX Service Manual - Manual (Page 87)

SECTION 3 - TROUBLESHOOTING
3120819 – 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. If a problem should
develop which is not presented in this section or which is
not corrected by listed corrective actions, technically qual-
ified guidance should be obtained before proceeding with
any maintenance.
3.2 TROUBLESHOOTING
The troubleshooting procedures applicable to the aerial
platform are listed and defined in Tables 3-1 through 3-6.
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 system,
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 (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 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