TM 5-6675-250-10
1-9. TECHNICAL PRINCIPLES OF OPERATION - Continued
b.
Electronic Control Unit (ECU)
(1)
Panel illumination control (1). Enables the operator to illuminate the panel during night use.
During day operations the control is rotated fully counterclockwise. To illuminate the panel
for night operations, the control is rotated clockwise.
(2)
Mode select switch (2). The MODE SELECT switch is maintained in the PWR OFF position
when the equipment is not in operation. Placing the switch in THEO ILLUM position lights
the telescope reticle, the scales, and the autocollimation eyepiece. Placing the switch in the
SELF TEST position enables the operator to perform assurance tests of the equipment
before and during operation. The determination and setting of bias conditions is accom-
plished with the use of the MODE SELECT switch in the BIAS position. Placing the switch in
GC (gyro compassing) applies power to the gyro motor and indicates the alignment operation
of the instrument. Through the BRAKE ON position, the gyro motor is stopped when it is
desired to repeat alignments or shut down the instrument. With the MODE SELECT switch in
the THEO ILLUM position, all system power is off except to the theodolite. In this mode the
theodolite may be used for determining azimuths from the original north determination, but
the azimuth should be verified by re-reading to the target after caging and braking of the gyro
wheel. In this mode the theodolite can also be used for any normal theodolite procedure.
Power on indicator (3). The system's power is on when the PWR ON indicator is lit. Failure
(3)
of the indicator to light when the ECU is connected to the power source, and when the MODE
SELECT switch is moved from the PWR OFF or THEO ILLUM positions, indicates a malfunc-
tion in the system.
Press to test switch (4). Press to obtain a TEST METER indication for each test position set-
(4)
ting of the TEST SELECT switch. Operation of the PRESS TO TEST switch is needed only dur-
ing the self-test procedure to obtain an indication on the TEST METER.
Test select switch (5). Used in conjunction with the TEST METER to check subsystems of
(5)
the equipment and stages of operation. During self-test operations, the selector switch is
placed to each of its positions. At each position the PRESS TO TEST switch is pressed and
operability of the associated circuit is indicated on the TEST METER (pointer in green area
for all but SOURCE VOLTAGE, which is displayed on the upper meter scale and GYRO, which
should center in yellow area).
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