JLG 660SJ ANSI Service Manual - Manual (Page 261)

SECTION 7 - SCHEMATICS
3120718 – JLG Lift – 7-1
SECTION 7. SCHEMATICS
7.1 GENERAL
This section contains schematics 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
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 best place to begin the problem analysis is at the
power source (pump). Once it is determined that the
pump is serviceable, then a systematic 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