Textron Jacobsen SLF530, Repair Manual

Page: 85 / 352

ELECTRICAL
673831-Rev A 4-41
4
Instrumentation Circuit—Theory of
Operation
Unswitched Power Circuit
Unswitched power is available from the battery positive
terminal to the 3-way distribution block.
Unswitched power is available from the 3-way distribution
block to the following:
• 30-amp fuse (F3)
• 15-amp fuse (F4)
• 30-amp fuse (F5)
• 20-amp (F6)
• 20-amp fuse (F7)
Unswitched power is available from 30-amp fuse (F3)
output terminal to the ignition relay (K1) terminal 30.
Unswitched power is available from 15-amp fuse (F4)
output terminal to the following components:
• Ignition switch terminal 6
• LDU Display terminal 1-01
Unswitched power is available from 30-amp fuse (F5)
output terminal to the fan motor (M4) terminal 1.
Unswitched power is available from 20-amp fuse (F6)
output terminal to the MCU (U1) terminals 6-06 and 6-07.
Unswitched power is available from 20-amp fuse (F7)
output terminal to the MCU (U1) terminals 1-01 and 1-01.
Switched Power Circuit (Green)
When the key switch (SW1) is turned to the run position,
voltage is provided from key switch terminal 4 to ignition
relay (K1) terminal
8 6, energizing the relay and to MCU
(U1) terminal 1-02.
With the ignition relay (K1) energized, switched power is
provided from ignition relay terminal
8 7 to the following
components:
• 2.5 k

engine temperature resistor (R2)
• 10-amp fuse (F 8 )
• 4WD Relay (K5) terminal 30
• Forward switch (SW10) terminal 1
• LDU (U2) terminal 1-03
With switched power provided to the MCU, the MCU will
energize.
Switched power is provided from 10-amp fuse (F 8 ) to the
following:
• Air ride seat (M3) terminal 4
• Fan relay (K4) terminal 30
With switched power provided to the LDU, the LDU
display will energize and will display vehicle status.
Fan circuit
Power flows through the 2.5 k

engine temperature
resistor (R2) to the engine temperature sensor (R5) and
the MCU (U1) terminal 3-02.
The engine temperature sensor (R5) resistance changes
in relationship to the engine coolant temperature. As the
engine temperature sensor is heated, the resistance of
the sensor changes from a high resistance to a low
resistance. The amount of resistance in the circuit is used
by the MCU as a temperature measurement.
When the engine temperature reaches 150° F (66° C),
the MCU will send power from terminal 2-04 to the fan
relay (K4) terminal
8 6, energizing the relay. When the fan
relay is energized, power will be provided from the fan
relay terminal
8 7 to the fan motor terminal 3. The fan will
start turning.
If the engine temperature drops below 74° F (23° C) or
the key switch is turned to the off position, the MCU will
stop supplying power to the fan relay terminal
8 6. The fan
relay will de-energize and the fan will stop.
Engine Oil Pressure Switch Circuit
When the engine oil pressure is below 7 psi (0.4 8 3 BAR),
the engine oil pressure switch contacts close. With the
switch contacts closed, a path to ground is provided to
the MCU (U1) terminal 6-11.
Parking Brake Solenoid
When the parking brake switch is in the on position, the
MCU (U1) provides power from terminal 2-05 to the
parking brake solenoid (SOL
8 ), energizing the solenoid.
LDU Alarm
When a fault is displayed, the LDU (U2) provides power
from terminal 1-11 to the horn (U5), sounding the horn.
4WD Circuit
The 4WD circuit is activated using the pop-up menu on
the LDU display. 4WD operation is communicated to the
MCU by the CAN circuit.
When the traction pedal is pressed in the forward
position, the pedal arm is brought near the magnetic
target zone of the forward proximity switch (SW10),
activating the switch. With the switch activated, voltage is
provided from the proximity switch to MCU (U1) terminal
4-03. When the signal is detected at terminal 4-03 and
the 4WD circuit is active on the LDU, the MCU will
provide power from terminal 5-07 to the 4WD solenoid,
energizing the solenoid. With the solenoid energized, all
four wheels will drive the mower in the forward direction.