JLG 120HX ANSI Service Manual - Manual (Page 90)

SECTION 3 - TROUBLESHOOTING
3-8 – JLG Lift – 3120686
TOWER LIFT AND UPRIGHT CIRCUIT (A MODELS
No response to control.
Function not activated within 7 seconds after
footswitch depressed. Recycle footswitch.
Tower lift control inoperative. Repair or replace control lever.
Hydraulic system oil low. Replenish oil as necessary.
Restricted or broken supply line on valve bank or
hydraulic pump. Clean or replace line.
No electric to control. See proper wiring diagram.
Control valve not functioning properly. Repair or replace valve.
Over center valve malfunction. Repair or replace valve.
Hydraulic pump not functioning properly. Repair or replace pump.
Tower lift and upright will not raise.
Function not activated within 7 seconds after
footswitch depressed. Recycle footswitch.
Load capacity exceeded (personnel or equip-
ment on platform. Reduce load. (Refer to capacity placard)
Hydraulic oil system low. Replenish oil as necessary.
Restricted or broken hydraulic line or fitting. Clean, repair, replace line or fitting.
Holding valve(s) on cylinder(s) not working. Replace holding valve(s).
Control valves not functioning properly. Repair or replace valve.
Pressure relief valve not functioning properly. Re-adjust or replace valve.
Bypass valve (dump) not functioning. Repair or replace valve.
Tower lift cylinder not functioning properly. Repair or replace cylinder.
Counterbalance valve not adjusted. Replace counterbalance valve.
Failed master cylinder. Repair or replace master cylinder.
Tower level cylinder not synchronized. Correctly adjust cam valves.
Tower lift and upright will not lower.
See: Tower lift and upright will not raise
No electric power to dump valve. Repair or replace valve.
Tower lift and upright raises and lowers erratically.
Hydraulic system oil low. Replenish oil as required.
Restricted or broken hydraulic line or fitting. Clean, repair, replace line.
Table 3-2.Boom Assembly - Troubleshooting
TROUBLE PROBABLE CAUSE REMEDY