TM 5-3805-280-24-1
Sub-System Diagnostics
MONITOR CONTROLLER AND DISPLAY CIRCUIT THEORY OF OPERATION
When the key switch is turned to ON, the monitor
The monitor controller and display (A5) contains
controller and display performs a lamp check by
gauges and indicators, sensor inputs, and switches.
illuminating all the status indicators. After 2 - 3
The gauges and indicators display the status of
seconds the lamp check mode ends, and indicator
machine systems and control switches. The sensor
lamp illumination is controlled by the sensor inputs.
inputs are used by the monitor controller to monitor the
status of the machine systems, and the switches are
AIR FILTER RESTRICTION INDICATOR LIGHT (H14)
used to control or select machine functions by
providing control signal outputs to other machine
The air filter restriction switch (B1) is a normally open
systems. The illumination of the indicators and the
switch that closes to machine ground when a
status of control signal outputs are controlled by logic
restriction is sensed with the engine running. The
circuits and drivers in the monitor controller in
machine ground is applied to controller terminal 3,
response to the sensor inputs and control switch
causing the indicator to illuminate.
settings.
9015
FUEL LEVEL INDICATOR LIGHT (H13)
Operating power to controller and display is applied
15
from monitor controller and display fuse F5 to
47
The fuel level switch (B2) is normally open when fuel
terminals 39 and 40. Cab frame ground is applied to
is in the tank, and closes to machine ground when the
terminal 37. Backup power for the controller logic
fuel level is below 112 mm (4.4 in.). The machine
circuits is applied from radio and monitor controller
ground is applied to controller terminal 2, causing the
fuse F1 to monitor controller terminal 39.
indicator to illuminate.
HOURMETER AND GAUGES
ENGINE COOLANT TEMPERATURE INDICATOR
LIGHT (H16)
Operating power for the hourmeter is applied from fuse
F5 to controller terminal 29, and the controller monitors
The engine coolant temperature switch (B3) is a
the alternator excitation field at terminal 42. When the
normally open switch that closes to machine ground
engine is running and the alternator excitation field
when the coolant temperature exceeds 105 5C (221
voltage is greater than 11.5 volts, the hourmeter
35F). The machine ground is applied to controller
operates.
terminal 1, causing the indicator to illuminate.
The engine coolant temperature and fuel level gauges
ENGINE OIL PRESSURE INDICATOR (H17)
(P2 and P3) are controlled by coolant temperature and
fuel level senders B9 and B8, which provide a variable
The engine oil pressure switch (B4) is normally closed
resistance to ground for the gauges.
and opens with the engine running. When the oil
pressure falls below 39 kPa (.039 bar) (5.7 psi) the
Temperature sender B9 is applied to controller terminal
switch closes to machine ground. The machine ground
47, and fuel level sender B8 is applied to terminal 46.
is applied to controller terminal 10, causing the
indicator to illuminate.
STATUS INDICATORS
Continued on next page
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