TM 5-6675-250-10
I
3-2. TROUBLESHOOTING - Continued
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
ELECTRONIC CONTROL UNIT (Continued)
b. Replace a defective ECU with a new one by disconnecting and
connecting power cables.
c. Report defective ECU to the next higher level of maintenance.
3. TEST METER FAILS TO INDICATE NULL WHEN BIAS CONTROLS ARE OPERATED.
Step 1.
Ensure that GRU is level.
a. Rotate the theodolite alidade to position the objective end of the
telescope over the NORTH mark on the GRU. Tighten the horizontal
lock. Preorient the GRU to north by releasing the tripod hold-down
clamps, and rotate the GRU in the tripod until the two magnetic com-
pass needle images coincide. With the telescope level, depress the
plunger on the magnetic compass. Check to ensure that the plumbing
pointer is still over the fixed reference point. Tighten each of the three
hold-down clamps on the tripod.
b. To obtain fine-leveling, rotate the theodolite alidade so that the long
axis of the plate level is in the same plane as one of the tripod legs.
Adjust the fine-level control to place the bubble in the center of the
level vial. Rotate the alidade 90 degrees and adjust both of the remain-
ing legs. Continue the process until the alidade can be rotated 360
degrees, with no more than 1/2 division displacement of the bubble.
Step 2. Check for defective ECU.
With MODE SELECT switch in SELF TEST and TEST SELECT switch
a.
in BIAS, depress PRESS to TEST switch for green area reading on
test meter.
Replace defective ECU with an ECU that is operable by disconnect-
b.
ing and connecting power cable.
Report a defective ECU to next higher level of maintenance.
c.
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