GYROSCOPIC REFERENCE UNIT

TM 5-6675-250-10

3-2. TROUBLESHOOTING - Continued

MALFUNCTION

TEST OR INSPECTION

CORRECTIVE ACTION

GYROSCOPIC REFERENCE UNIT (GRU) (Continued)

b. Replace a defective ECU with a new one by disconnecting and

connecting power cables.

c. Report a defective ECU to the next higher level of maintenance.

3 . THEODOLITE RETICLE AND OPTICAL LAMPS FAIL TO LIGHT WHEN MODE SELECT

SWITCH IS PLACED TO THEO ILLUM AND THEO BRT CONTROL IS ROTATED

CLOCKWISE.

Step 1. Check for defective lamp(s).

a. Ensure that the power is off.

b. Rotate the applicable protective cap counter-clockwise and remove.

c. Remove the lamp from the socket.

d. Visually inspect lamp for a burned out filament. If filament is defec-

tive, replace with a new lamp.

e. Place the good lamp in the socket.

f. Position the protective cap over the socket and turn clockwise until

finger-tight.

Step 2. Check for a defective power cable.

a. Disconnect the power cable from the receptacle on the ECU and

power source.

b. Inspect power cable for damaged connectors and broken or frayed

wires and insulation. Replace damaged power cable.

c. Connect the power cable to the power source and ECU receptacle.

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