JLG 150HAX Service Manual - Manual (Page 148)

SECTION 6 - SCHEMATICS
6-20 – JLG Lift – 3120817
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.
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 safety 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.
Abrupt start-up of any functions: both directions.
Card “Low” potentiometer setting too high. Adjust “Low” potentiometer to “Just Start” func-
tion.
“High” and “Low” pots set too close
together. Adjust per PQ Publication 3120304.
Slow function speed/engine lugs down at full throw handle position.
Card “High” potentiometer set too low. Adjust “High” potentiometer until function speed
does not lug down.
Table 6-6.Electrical System - Troubleshooting
TROUBLE PROBABLE CAUSE REMEDY