JLG 120HX Service Manual - Manual (Page 105)

SECTION 3 - TROUBLESHOOTING
3120819 – JLG Lift – 3-19
Regardless of which way handle is moved, only one function occurs.
Improper wiring or loose wiring to the solenoids
or potentiometer. Check all wiring for proper connections.
Printed circuit board failure. Replace printed circuit board or use a handle
assembly from a circuit that is presently working
to check valve.
Potentiometer needs adjusted. Adjusted potentiometer as required.
Spool stuck in valve bank. Clean/replace spool.
Function occurs very rapidly when handle is moved in one direction and very slowly when moved in the opposite direction.
Improper null of the handle. Check and re-adjust null.
Potentiometer off-center. Center potentiometer.
Defective printed circuit board. Replace printed circuit board.
Valve will not function when handle is moved in either direction.
No electrical power to handle. Check electrical input to handle (12V).
No electrical signal to valve. Check electrical valve output of printed circuit
board and electrical signal at the valve. Repair or
replace wiring or circuit board as necessary.
Failed printed circuit handle. Replace square wave generator or use a handle
assembly that is presently working in the system.
Failed open control handle safety deadman
switch. Check and replace deadman switch.
Improper ground. Check for proper grounding of handle.
Failed microswitch. Replace microswitch.
No pilot oil at valve. Check pressure reducing valve and adjust if
needed.
No sequence pressure at valve. Check pressure reducing valve and adjust as
needed.
No oil volume at valve bank. Check pump for failure.Check hydraulic oil level.
Failed or stuck port relief. Clean or replace port relief.
Functions occur in the opposite direction than required in regard to handle movement.
Valve coils are reversed. Reverse control valve coils.
Coil wires are reversed. Reverse coil wires.
Hydraulic hoses reversed. Refer to hydraulic diagram for proper hosing.
Table 3-6.Electrical System - Troubleshooting
TROUBLE PROBABLE CAUSE REMEDY