JLG sky trak mmv Service Manual page 343

Before troubleshooting any
hydraulic circuit, ALWAYS
begin by checking the
following:
1. Hydraulic oil level in the
reservoir
2. All hoses, tubes, fittings
for leaks, kinks,
interference, etc.
3. Air in the lines
NOTE:
When checking pressures in
circuits, refer to Section 9.7,
Hydraulic System Testing for
correct pressure readings.
Model MMV Rev. 12/04
If the attachment tilt cylinder
retracts slowly, check pilot
pressure at main control valve.
Check solenoid valve cartridge
in pilot select manifold.
If OK
Check port relief at
main control valve.
If OK
Check pilot pressure at "PPG" port
of secondary function manifold.
If OK
Check main relief pressure at "VG"
port of unloader valve.
If OK
Check differential pressure sense
valve on the unloader valve.
If OK
Check pump flow.
If OK
Isolate and check each slave
cylinder for packing leaks.
If OK
Check the counterbalance and the
pilot-operated check valves on the
attachment tilt cylinder.
If OK
Check packing in attachment
tilt cylinder.
If the attachment tilt cylinder
drifts and does not hold load,
check the counterbalance valve
on the attachment tilt cylinder.
If OK
Isolate and check packing in
each slave cylinder.
If OK
Check packing in attachment
tilt cylinder.
Hydraulic System
Refer to Section 10.7.20,
Not
Attachment Tilt Mode Circuit and
OK
Troubleshooting.
If OK
Not
Replace solenoid cartridge.
OK
Adjust/repair/replace the relief
Not
valves on attachment tilt section of
OK
main control valve.
Adjust, repair or replace the
Not
pressure reducing cartridge on the
OK
secondary function manifold.
Adjust/repair/replace relief valve
Not
OK on unloader valve.
Adjust/replace differential pressure
Not
sense valve on unloader valve.
OK
Not
Repair/replace pump.
OK
Not
Repair/replace slave cylinder(s).
OK
Replace counterbalance and/or
Not
pilot-operated check valve(s).
OK
Repair/replace attachment
Not
OK tilt cylinder.
Replace counterbalance valve on
Not
OK attachment tilt cylinder.
Not
Repair/replace slave cylinder(s).
OK
Repair/replace attachment
Not
OK tilt cylinder.
9.45