Repair manual

Steering and Pitch Control CRT Repair
wc_tx000584gb.fm 82
7.9 Electric Steering System Background
See Graphic: wc_gr003372
Movement of the trowel is dependent on the angle of the gearboxes.
The actuators are the mechanical devices which adjust the angle of
each gearbox. An electric motor mounted to each actuator spins and
as it does it turns the actuator’s main drive screw in or out. This
movement of the actuator’s main drive screw changes the angle of the
gearbox.
Control of power to the actuator motors is done through electric signals
(voltages) sent and received between the major components of the
system: the joysticks, the control board, the actuator motors, and the
load pins.
When the ignition key is in the ON position, the joysticks receive
12VDC from the control board and feed back 0–5VDC depending on
their position. In the home position (neutral), they hold a 2.5VDC
charge. In the full-forward position, the voltage approaches 5VDC; in
the full-backward position, the voltage drops to approximately 0.5VDC.
The load pins are also fed 12VDC from the control board and feed back
0–5VDC. The amount of voltage fed back to the control board depends
on the amount of force applied to them by the actuator. The greater the
pressure, the greater the voltage feedback to the control board. In the
home position (neutral) the load pins are preloaded and hold a 2.5VDC
charge. As the angle of the gearbox changes, so does the pressure on
the load pin. When the gearboxes are tilted forward, the pressure on
the load pins decreases. This decrease in pressure translates into a
decrease in the feedback voltage to the control board. When the
gearboxes are tilted backward, the pressure on the load pins
increases. This increase in pressure increases the feedback voltage to
the control board.
For every feedback voltage from the joysticks, the control board is
programmed to expect a specific feedback voltage from the load pins.
For every position of the joysticks, the control board will send voltage
to the appropriate actuator motor until the pressure on the load pin
translates into the expected feedback voltage for the given position; at
which point, voltage to the actuator motor ceases and actuator
movement stops.