JLG 15VPSP Service Manual - Manual (Page 85)

SECTION 3 - TROUBLESHOOTING
3120728 – JLG Lift – 3-31
Platform Will Not Lower From Ground Control Toggle Switch
Overview Of Procedure
The following procedure examines the complete ground control circuit from the battery all the way to the pump motor for
wiring or components which could be causing a failure of that circuit.
Check For These Obvious Conditions First:
• Battery voltage 24 volts. (Fully charge batteries)
• Battery connections clean and tight.
• Key switch positioned to Ground (GRND) control.
• Emergency stop switch set to the Reset position)
• Ground control power supply and wiring, OK (Table 3-4).
• 5 amp fuses on power and pump circuits, OK.
• Hydraulic oil level, OK.
Table 3-25. Unit Will Not Lower From Ground Control Toggle Switch.
STEP ACTION SPEC YES NO
1. Will machine lower manually? — Go to Step 3 Go to Step 2
2. Check for obstructions in the mast, cylinder, hydraulic lines and lift
down valve.
—
Repair, Replace
or Adjust
Go to Step 3
3. Check terminal 30 and 85 on the ground control relay for ground. Is
ground contact OK? Continuity with B–.
Ground Go to Step 4
Repair Wiring or
Connection
4. Check continuity across terminals 87 and 30 on the ground control
relay. Is there continuity? (Relay must be energized)
Ground Go to Step 5 Replace Relay
5. Check the Black wire from terminal 87 on the ground control relay to
the lift up/down ground control switch. Is there continuity with B –?
— Go to Step 6
Repair Wiring or
Connection
6. Check for continuity across the terminals (Black to Tan, 4-1 wire) of
the lift up/down ground control toggle switch. Is there continuity
with the switch activated?
— Go to Step 7
Replace Lift Up/
Down Ground
Control Switch
7. Check the Tan, 4-1 wire for continuity from the lift up/down ground
switch to the lift-down coil. Is there continuity?
— Go to Step 7
Repair Wiring or
Connection
8. Check the Yel/Red, 2-6 wire from the pump motor to the lift-down
coil for voltage. Is there voltage?
24 volts —
Repair Wiring or
Connection