Installation. - TM-5-6675-250-340128

TM 5-6675-250-34

Installation.

( 5 ) Inspect for visual evidence of corrosion of

(1) Install the anti-backlash setting tool (fig. 4-

o t h e r defects.

3) into the index hole of the upper gear of the follow-

b. Adjust (fig. 4-4).

(1) To keep foreign particles from entering the

u p gear set, the handle of the tool towards main

c o n n e c t o r cover.

i n n e r parts of the instrument, place masking tape

between the housing and the inner shield, except in

(2) Place the thumb on one end of the gear set

the area of the caging link.

and the index finger on the other and slide the two

( 2 ) Set the instrument on the work surfaces,

gear halves together so the ends are flush.

( 3 ) Press and anti-backlash setting tools into

resting on the inner shield and in the upright

t h e index of lower gear half and relax the thumb

position. Be careful not to damage the shield as the

a n d index finger.

shield material is very soft and sensitive to shock.

(4) Connect the gearbox assembly electrical

( 3 ) Loosen the caging link jam nut (fig. 4-4).

cable connector to the female receptacle on the

( 4 ) Install the cage-uncage knob temporarily,

housing connector. Rotate the cable connector

s o that the caging mechanism may be actuated.

m o u n t i n g screws in the clockwise direction, being

(5) Connect the GRU to the ECU and apply

careful to alternate between the two screws after (2

p o w e r in the BIAS mode.

to 3) turns.

(6) Rotate the cage-uncage knob until the

(5)

Place

the

cable

between

the

gearbox

c a g i n g cam arm passes over center of the caging

l i n k . At the point where arm crosses over center,

assembly mounting pads, so that it will be under the

g e a r b o x when the gearbox in in final position.

o b s e r v e that a small gap (approximately 1/64-inch)

i s present between the head of the shoulder screw

( 6 ) Rotate the follow-up shaft to the extreme

c l o c k w i s e position by turning theodolite mounting

a n d the upper clevis.

plate.

(7) If the gap described in step (6) is not

correct, rotate the length adjuster counterclockwise

( 7 ) Install the gearbox assembly through the

access and place it so that the mounting screw holes

t o increase the gap and clockwise to decrease the

are lined up.

gap.

(8) Prepare the three gearbox assembly

(8) Continue rotating the cage-uncage knob

m o u n t i n g screws (para 2-10a).

until the caging arm guide pin (fig. 4-8) moves

about 1/32-inch in the guide slot. The uncaged indi-

(9) Install the screws but do not tighten.

cater should light at that point. If the indicator does

(10) Press the gearbox assembly against the

index pins (fig. 4-3) on the inner mounting pads and

not light at the proper point, refer to para 4-12, 4-13,

tighten the mounting screws while maintaining the

a n d 4-14 for instructions on adjusting the caging

g e a r b o x position.

control

switches.

(11) Remove the anti-backlash setting tool from

CAUTION

The pendulum is now uncaged, being

the indexing hole,

( 1 2 ) Prepare the ten (10) access cover mount-

supported by a metal band. Leave the in-

strument in the upright position and handle

ing screws (para 2-10a).

it gently while in this state.

(13) Install the gearbox assembly access cover.

(9) With the caging arm switch actuating pin in

( 1 4 ) Install the main connector housing cover.

c. Test. T e s t g e a r b o x b y s e t t i n g u p t h e i n -

the proper position and the uncaged indicator

lighted, rotate the cage-uncaged knob coun-

struments as for operation and check for proper

meter indication and follow-up shaft rotation in the

t e r c l o c k w i s e to cage the pendulum.

servo positions during self test. Refer to TM5-6675-

(10) Observe the caging cam arm to see whether

250-12.

or not it has gone over center. If it has gone over

center rotate the length adjuster (fig. 4-4) coun-

4-6. Caging Mechanism.

t e r c l o c k w i s e until the caging arm does not go over

a. Inspection.

c e n t e r when repeating step (9).

( 1 ) Remove the cage-uncage knobby loosening

(11) With the caging cam arm going over center

t h e two knob setscrews.

when the pendulum is caged, rotate the length

(2) Remove the caging mechanism cover by

adjuster 1/16 turn clockwise and repeat the un-

r e m o v i n g twelve (12) cover attachment screws.

c a g i n g and caging process.

( 3 ) Lay the GRU on its side and remove the

(12) Repeat (11) until the caging cam arm just

t r i p o d by backing out the three tripod attachment

g o e s over center, then rotate the length adjuster

screws

and

sliding

back

the

tripod

hold-down

a n o t h e r 1/16 turn clockwise.

damps.

( 1 3 ) Tighten the jam nut and repeat the un-

( 4 ) Remove outer shield (para 4-4).

4 - 6 , Change 1