JLG 600SC_660SJC Service Manual - Manual (Page 169)

SECTION 7 - SCHEMATICS
3120898 – JLG Lift – 7-1
SECTION 7. SCHEMATICS
7.1 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.
7.2 TROUBLESHOOTING
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.
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.
7.3 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.