JLG 20VP (3120728) Service Manual - Manual (Page 90)

SECTION 3 - TROUBLESHOOTING
3-30 – JLG Lift – 3120728
3.9 MAST TROUBLESHOOTING
Platform Will Not Lift Up Using Platform Control
Overview Of Procedure
This procedure examines the complete pump motor, ground control and pump valves electrical circuits.
Check For These Obvious Conditions First:
• Battery voltage 24 volts. (Fully charge batteries)
• Platform loaded within maximum allowable capacity.
• Hydraulic oil is within it’s specified operating temperature range.
Table 3-20. Platform Will Not Lift Up Using Platform Control.
STEP ACTION SPEC YES NO
1. Will platform lift from ground control switch?
Note: Key switch must be set to GRND to test this.
— Go to Step 2 See (Figure 3-24)
2. Does pump motor run?
— Go to Step 3
See Pump Circuit
Check
(Table 3-21 )
3. Are the down and dump valves opening/closing properly?
Note: If machine will not lift and hydraulic oil is visible flowing in the
hydraulic tank, the dump valve is stuck in the open position.
— Go to Step 4
See Pump Valves
Circuit Check
(Table 3-22 )
4. Is the pressure set properly on the pump?
— Go to Step 5
Set to correct
pressure specifi-
cation per this
Service Manual
5. Is the lift cylinder OK?
— Go to Step 6
Rebuild or
Replace Lift Cyl.
6. Are the mast sections operating freely?
—
Consult
Factory
Check Mast,
Rebuild
if Necessary