JLG 120-SXJ ANSI Service Manual - Manual (Page 47)

SECTION 3 - CHASSIS & TURNTABLE
3121105 – JLG Lift – 3-19
3.7 LOAD MANAGEMENT SYSTEM
ADJUSTMENT
1. With boom retracted, limit switch and proximity
switch are in neutral position.
2. Extend boom in horizontal position until white tape
on inner mid boom is fully exposed, no load in plat-
form.
3. Adjust proximity switch target until LED light comes
on (switch is tripped), then secure locking nut.
4. Adjust actuator to trip switch, then secure locking
nut.
5. To test cutoff switches, retract boom to reset posi-
tion, then extend boom to test cutoff. Do not extend
boom past white tape.
6. To test limit switch, retract boom to reset, then
extend boom to cutoff while holding test bypass
switch in “M” position. To test proximity switch,
retract boom to reset, then extend boom to cutoff
while holding test bypass switch in “P” position.
When testing switches, do not extend boom past
white tape on inner mid boom.
3.8 TURNTABLE SPRINGS
Removal
1. Fully retract boom.
2. Remove rear turntable cover.
3. Remove five (5) nuts and jam nuts from beneath
turntable which attach to turntable spring bolts.
4. If necessary, remove bolts which secure load man-
agement switches to mounting bracket and allow
switches to hang freely.
WRAP MASKING TAPE AROUND THE LOAD MANAGEMENT
SWITCHES TO INSURE THAT THE SWITCHES WILL STILL BE
OPERABLE.
5. Position boom to horizontal.
6. Remove five (5) bolts and turntable springs from
turntable.
Installation
1. Position boom to horizontal.
2. Install five (5) bolts and turntable springs onto turn-
table.
3. Install five (5) nuts and jam nuts on turntable spring
bolts.
4. Extend boom to cutoff (white tape) position then
retract boom until turntable raises 1/4 in. (6.4 mm)
from cutoff position, measured at spring area.
5. Snug jam nuts, then fully retract boom.
6. Torque jam nuts to 75 ft. lb. (10.4 kgm), then tighten
nuts.
7. If removed, install load management switches on
mounting brackets.
8. Position boom to horizontal. Adjust load manage-
ment switches as required.
3.9 DRIVE AND STEER CONTROLLER
Controller Theory & Definitions
This controller is specifically designed and manufactured
to provide a proportional output to a SUNDSTRAND Dual
Coil electro-hydraulic valve. The controller you are about
to calibrate has the following features:
PWM Output (Pulse \Width Modulation)
The SUNDSTRAND valve being driven by this controller
requires an electrical current, between 20 and 130 milli-
amps in order to shift the valve spool from minimum to
maximum flow. Because of the mass of the spool, shifting
it a very small distance would be very difficult to do with-
out overshooting the mark. This overshoot is called hys-
teresis and makes precise control of the function very
difficult. PWM output provides a pulsed current to the
spool which actually vibrates the spool so that it is never
at rest and very easy to shift. This controller pulses the
spool 100 times (cycles) per second and as you move the
handle, the electronics change the time period the pulse
is on within that cycle. As you move the handle away from
center, the on time period or width of the cycle pulse will
increase and as you move the handle back towards the
center, the pulse will decrease. The percentage of on time
to off time of the PWM signal is called the Duty Cycle, if it
is on for 80% we call that an 80% duty cycle.