JLG 120HX ANSI Service Manual - Manual (Page 88)

SECTION 3 - TROUBLESHOOTING
3-6 – JLG Lift – 3120686
Boom extends and retracts erratically.
Hydraulic system oil low. Replenish oil as necessary.
Wear pads worn. Replace pads as required.
Restricted or broken hydraulic line or fitting. Clean, repair, or replace line or fitting.
Control valve not functioning properly. Repair or replace valve.
Worn seals in telescope cylinder. Replace seals.
Cylinder not functioning properly. Repair or replace cylinder.
Counterbalance valve not functioning properly. Replace counterbalance valve.
TOWER TELESCOPE SYSTEM (A MODELS
Tower telescope cylinder will not extend.
Function not activated within 7 seconds after
footswitch was depressed. Recycle footswitch.
Tower lift cylinder not fully elevated. Fully elevate tower lift cylinder.
Cam valves out of adjustment. Correctly adjust cam valves.
Tower level cylinder not synchronized. Correctly adjust cam valves.
Defective cylinder or binding boom. Repair or replace cylinder or defective boom
parts.
Tower lift cylinder will not lower.
Function not activated within 7 seconds after
footswitch was depressed. Recycle footswitch.
Tower telescope cylinder not fully retracted. Fully retract tower telescope cylinder.
Cam valves out of adjustment. Correctly adjust limit cam valves.
Defective cylinder or binding boom. Repair or replace cylinder or defective boom
parts.
No response to control.
Function not activated within 7 seconds after
footswitch was depressed. Recycle footswitch.
Valve spool sticking. Repair or replace valve.
Poor ground on valves. See proper wiring diagram.
No electric power to dump valve on cylinder. See proper wiring diagram.
No electric power to valves. See proper wiring diagram.
Internal damage to cylinder. Repair or replace cylinder.
Table 3-2.Boom Assembly - Troubleshooting
TROUBLE PROBABLE CAUSE REMEDY