Electrical System - TM-5-6675-250-340016

TM 5-6675-250-34

unit and the reference unit to be tested prior to the

CAGE-UNCAGE knob on the outside of the

housing.

azimuth determination procedure. A PRESS TO

TEST switch and TEST METER are used in con-

(2) The pendulum is a tubular structure with the

top end capped with a mounting plate for the

junction with the TEST SELECT switch to obtain

indications of circuit operation. Through the PRESS

suspension band clamp and the lower end is fitted

TO TEST switch, the output of circuits under test

with the gyro wheel assembly. Surrounding the full

length of the pendulum is a tubular structure called

are connected from the calibration circuit to the

TEST METER. Satisfactory operation of the cir-

the air damper, that is attached to the lower end of

cuits corresponding to the TEST SELECT switch

the follow-up shaft. The purpose of the air damper is

to suppress lateral pendulum motion through

positions (fig. 1-2) are indicated on the TEST

pneumatic damping. In the uncaged condition, the

METER and as specified in test procedures.

pendulum is suspended by a thin metal band which

Lighting provisions of the unit are activated with the

extends from the top of the follow-up shaft to the top

initial application of power.

of the pendulum. Caging of the lower end of the

1-10. Electrical System (Fig. 1-6 and 1-7).

pendulum is furnished by a tapered seat on the

a. General. The electrical system is contained in

pendulum that rests on a similar seat on the air

the ECU and GRU. Cable assemblies are provided to

damper. The pendulum and air damper is isolated

interconnect the two units and to connect the control

from magnetic fields by a mu-metal shield which is

unit to a power source. Unregulated dc power is

attached to the lower side of the housing.

connected at the INPUT POWER receptacle 2A2J2

c. Control of the aximuth determination procedure

of the ECU to provide operating power to the

is provided through the ECU. Power supplied to the

SIAGL. The INTERCONNECT receptacle 2A2J3 is

input receptacle is distributed to the printed circuit

connected, through a two-branch wiring harness, to

board and chassis-mounted components through the

controls and indicators on the front panel, chassis-

MODE SELECT switch. Unregulated input voltage

mounted transformer 2A2T2, and to the card strip

is regulated in ac and dc supply circuits in the

connectors 2A2J5 and 2A2J6. Additional harnesses

system. Corresponding to the position of the

connect submodules, controls, and indicators to the

switches on the control unit, operating power is

card strip connectors 2A2J5 and 2A2J6. In the

applied to the GRU through the interconnect cable.

GRU, one wiring harness interconnects receptacle

F e e d b a c k signals from the GRU reflecting

1A1J1 to components in the follow-up and upper

gyroscopic action are applied to the printed circuit

housing assemblies. The harness also connects the

board. Subcircuits on the printed circuit board in-

26 Vac reference voltage for the excitation coils and

clude a gyro sync sensor, digital timing, and

the varied voltage for the torquer reference coil

reference voltage circuits. In operation of the

through separate power bands. From receptacle

SIAGL, derived signals from the printed circuit

1A1J1 the signal voltages to the servo motor and

board activate GYRO SYNC and READ

gear train assembly are connected by a sleeved cable

AXIMUTH indicators on the control unit panel. A

through connector 1A1J2.

self-test mode of operation enables both the control

Figure 1-6. Functional block diagram.

(Located in back of manual)

b. Detailed Description. All ac and dc operating

SELECT switch. The following paragraphs describe

voltages used in the system are derived from the

the operation of the equipment for each of the five

nominal 24 Vdc input. Through a fuse in the power

activated positions of the MODE SELECT switch.

input circuit, input voltage is applied to the MODE

Figure 1-7. Electronic control unit schema tic diagram (Sheet 1 of 5).

(Located in back of manual).

Figure 1-7. Electronic control unit schematic diagram (Sheet 2 of 5).

(Located in back of manual).

Figure 1-7. Electronic control unit schematic diagram (Sheet 3 of 5).

(Located in back of manual).

Figure 1-7. Electronic control unit schematic diagram (Sheet 4 of 5).

(Located in back of manual).

Figure 1-7. Electronic control unit schematic diagram (Sheet 5 of 5).

(Located in back of manual).

1-8

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