TM 5-3805-281-24-1
Sub-System Diagnostics
MONITOR CONTROLLER AND DISPLAY CIRCUIT THEORY OF OPERATION
AIR FILTER RESTRICTION INDICATOR LIGHT (H14)
The monitor controller and display (A5) contains
gauges and indicators, sensor inputs, and switches.
The air filter restriction switch (B1) is a normally open
The gauges and indicators display the status of
switch that closes to machine ground when a
machine systems and control switches. The sensor
restriction is sensed with the engine running. The
inputs are used by the monitor controller to monitor the
machine ground is applied to controller pin 3, causing
status of the machine systems, and the switches are
the indicator to illuminate.
used to control or select machine functions by
providing control signal outputs to other machine
FUEL LEVEL INDICATOR LIGHT (H13)
systems. The illumination of the indicators and the
status of control signal outputs are controlled by logic
The fuel level switch (B2) is normally open when fuel
circuits and drivers in the monitor controller in
is in the tank, and closes to machine ground when the
response to the sensor inputs and control switch
fuel level is below 112 mm (4.4 in.). The machine
settings.
ground is applied to controller pin 2, causing the
9015
indicator to illuminate.
Operating power to the controller and display is
15
applied from monitor controller and display fuse F6 to
47
ENGINE COOLANT TEMPERATURE INDICATOR
pin 40. Cab frame ground is applied to pin 37. Backup
LIGHT (H16)
power for the controller logic circuits is applied from
radio and monitor controller fuse F1 to monitor
The engine coolant temperature switch (B3) is a
controller pin 39.
normally open switch that closes to machine ground
when the coolant temperature exceeds 105 5C (221
HOURMETER AND GAUGES
35F). The machine ground is applied to controller
pin 1, causing the indicator to illuminate.
Operating power for the hourmeter is applied from fuse
F6 to controller pin 29, and the controller monitors the
ENGINE OIL PRESSURE INDICATOR (H17)
alternator excitation field at pin 42. When the engine is
running and the alternator excitation field voltage is
The engine oil pressure switch (B4) is normally closed
greater than 11.5 volts, the hourmeter operates.
and opens with the engine running. When the oil
pressure falls below 39 kPa (.039 bar) (5.7 psi) the
The engine coolant temperature and fuel level gauges
switch closes to machine ground. The machine ground
(P2 and P3) are controlled by coolant temperature and
is applied to controller pin 10, causing the indicator to
fuel level sensors B9 and B8, which provide a variable
illuminate.
resistance to ground for the gauges.
HYDRAULIC OIL LEVEL INDICATOR (H12)
Temperature sensor B9 is applied to controller pin 47,
and fuel level sensor B8 is applied to pin 46.
Hydraulic oil level switch (B5) is a normally open
switch, held closed when the oil level is adequate.
STATUS INDICATORS
When closed, the switch applies machine ground to
controller pin 9. The monitor controller only checks the
When the key switch is turned to ON, the monitor
status of pin 9 when the fluid level switch (S5) is
controller and display performs a lamp check by
pressed. If ground is present when the switch is
illuminating all the status indicators. After 2--3
pressed, the indicator illuminates.
seconds the lamp check mode ends, and indicator
lamp illumination is controlled by the sensor inputs.
Continued on next page
CED,OUOE012,27 1926JAN991/3
