JLG 120HX Service Manual - Manual (Page 77)

SECTION 2 - PROCEDURES
3120819 – JLG Lift – 2-55
Immediately beyond this point of balance the turntable is
permitted to pivot a maximum vertical distance of 3 mm.
This movement is sensed by two independent switches
which power two independent control circuit channels.
1. A positive break mechanical limit switch.
2. An inductive proximity switch.
Each circuit channel is arranged as follows:
The switch provides a 12 volt dc signal to a circuit card.
The output from this card energizes a relay which permits
the functional signals for boom extend and descend.
When an input signal to a channel or an output signal
from a circuit card is not present, the lift down and tele-
scope out functions are interlocked.
There is also a warning horn signal present, at both the
platform console and ground box, when either channel is
not energized.
Overmoment Control Monitoring System
The 12 volt dc input signals from the overmoment control
sensing switches are constantly monitored and compared
with the output from the circuit cards by the monitoring
system circuit.
If any fault is detected (input to output on the same chan-
nel or input to output on different channels) all movements
of the platform that could increase instability (lift up, lift
down, telescope out) are shut down and the boom permit-
ted to retract and descend in a controlled sequence. The
machine will remain in this state until reset by a competent
person.
The monitoring system operates as follows:
There is an output of 12 volts dc at terminal 7 on the over-
moment circuit card only after the input at pin No 2 has
received a 12 volt dc signal (from a sensing switch) for a
time duration greater than 3 seconds and this output sig-
nal will continue 0.5 seconds after the input signal is
removed.
These input signals also energize two independent 12 volt
timer relays (1 second delay off relay B) which control the
output signals from both circuit cards. If the input is
removed the timer relay B will de-energize after 1 second.
If an output signal from either card remains it will energize
two lockout latching relays (relay C). These relays control
the function signals to lift, lower, and extend the boom.
Therefore, when the latching coils receive a signal the
operator is permitted to retract the platform, to within 3
meters of the fully retracted position. This will enable oper-
ation of the boom lower function to bring the platform to
the ground level position. The machine will remain in this
condition (i.e. in the lowered position) until reset by a
competent person.
NOTE: The monitoring system only activates when there is
a malfunction of the overmoment control system.
Load Management System Daily Check
At the beginning of each days’ use, perform check with no
load (persons or material) in platform from ground control
station.
1. Extend all axles fully and insert lock pins (if applica-
ble).
2. With boom fully retracted, raise boom to horizontal.
3. Position toggle switch located on the right side of
the ground control station in the “P” position and
hold.
4. Extend boom until it stops. Boom must stop on
white tape on mid boom. Release toggle switch.
5. Retract boom 3 meters and attempt to extend boom.
boom must not extend. Reset system by activating
toggle switch marked “R” located on right side of
ground control station.
6. Position toggle switch located on the right side of
the ground control station in the “M” position and
hold.
7. Extend boom until it stops. Boom must stop on
white tape on mid boom. Release toggle switch.
8. Retract boom 10 feet (3 meters) and attempt to
extend boom. Boom must not extend. Reset system
by activating toggle switch marked “R” located on
right side of ground control station.