JLG 20VP (3120728) Service Manual - Manual (Page 77)

SECTION 3 - TROUBLESHOOTING
3120728 – JLG Lift – 3-17
3.7 MAIN POWER CIRCUIT TROUBLESHOOTING
Unit Will Not Power Up From Ground Control
Overview Of Procedure
The following procedure tests the circuits from the Battery (+) terminal through the Ground Control Box and to the Main
Contactor Relay and Main Contactor for 24 volts or more. Also the Lift Up/Down Relay circuit is tested.
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 pulled out. (Reset Position)
Table 3-4. Unit will not Power Up From Ground Control.
STEP ACTION SPEC YES NO
1. Check the 5 amp inline fuse on the Red 1-1 wire from the battery (+)
terminal to the ground control box, key switch.
(Under pump/motor cover).
24 volts OK, go to Step 2 Replace Fuse
Ground Control Box Assembly (Disassembled)
2. Is there 24 volts or more reading at the key switch, terminal B.
24 volts Go to Step 3
Check Wiring
from Battery to
Terminal B.
Repair or Replace
3. Check for 24 volts or more on the Yel/Red, 2-7 wire from the key
switch to the E-stop switch.
24 volts Go to Step 4
Repair wiring or
Replace Key
Switch
4. Check for 24 volts or more on the Yel/Red, 2-8 wire from the E-stop
to the Ground Control Relay, terminal 86.
— Go to Step 5
Repair wiring or
Replace E-Stop
Switch
5. Check for 24 volts or more on the Yel/Red, 2-4 wire from the E-stop
to the Main Contactor Relay, terminal 87.
— Go to Step 6
Repair wiring or
Replace E-Stop
Switch
Main Contactor Circuit
6. Check for 24 volts or more on the Yel/Red, 2-4 wire from the Main
Contactor Relay, terminal 87 to the Main Contactor.
— Go to Step 7
Repair wiring or
Replace Main
Contactor Relay
7. Did Main Contactor close? — Go to Step 9 Go to Step 8
8. Is the Black ground wire connection from the Main Contactor to
ground OK?
—
Replace Main
Contactor
Repair Ground
Wiring
9. At this point, 24 volts should be present at the following terminal
points;
• Terminal 86 on the Ground Control Relay.
• Main Contactor, Yel/Red, 2-4 wire. — — —
10. With Main Contactor engaged, 24 volts or more should be present at
the following terminal points;
• Pump Motor - 21’ cable #1.
• Yel/Red, 2-6 wire on the Pump Contactor.
• Yel/Red, 2-6 wires on the Lift Up/Down Relay. — — —