JLG 120-SXJ ANSI Service Manual - Manual (Page 45)

SECTION 3 - CHASSIS & TURNTABLE
3121105 – JLG Lift – 3-17
This circuit card operates as follows:
A calibrated dc voltage representing the boom angle is
sent from the boom angle sensor to the angle cosine cir-
cuit. This voltage is converted to the cosine of the angle
and presented to the radius generator circuit.
A calibrated dc voltage representing the boom length is
sent from the boom length sensor to the boom length cir-
cuit and presented to the radius generator circuit.
The length and cosine dc voltages are multiplied together
in the radius generator circuit. The output dc voltage from
this circuit is passed to a radius limiting circuit. This circuit
is set to detect a specific boom radius dimension. The
resultant output signal is sent to a logic network circuit
which determines which of the indicator lamps (blue or
red) should be energized.
There should be a signal from the sensors at all times,
however, if the signal line from the angle, or the boom
length sensor is cut a failure circuit detects this and acti-
vates an audible warning horn mounted in the console
panels.
The boom length circuit also produces output dc voltage
when the boom is within a predetermined critical boom
length. This signal energizes a 12 volt dc solenoid flow
control valve (via a relay in the overmoment control circuit
card) to enable the descend function to operate at full
speed. When this signal is removed, the descent function
defaults to a creep speed.
Also, when an overmoment condition is sensed by the
overmoment control circuit, a signal is sent to the logic cir-
cuit network. This causes either the red or blue lamp to
flash indicating that an overmoment condition exists in
that region. This condition also causes the audible warn-
ing to sound at the control consoles.
Overmoment Control System
The turntable is pivoted at the lower front area and com-
pression springs, mounted towards the rear, provide a
reaction force to the moment produced by boom exten-
sion. The force produced by the springs is adjusted to bal-
ance the moment produced when the boom is extended
to the maximum permitted radius.
Figure 3-12. Control Box Components