Station Selector Circuit Test

Polarity Test

The 14-15 winding of T2 at both stations couples

the incoming speech to the tapped windings of T2,

To test the polarity of the unit, operate polarity test

which include volume controls S25. Thus, the incoming

switch S214 (fig. 7-30) to the OK WHEN LIT position

signals appear across terminal 7 of T2 and the moving

(not shown). Indicator lamp 1210 should light with full

contact of volume control S25 at both stations. These

intensity if the polarity is correct. Now operate polarity

signal sources are connected in series addition through

test switch S214 to the REVERSED position (not

a closed loop containing both loudspeakers.

shown). The indicator lamp should go out if the polarity

The circuit is from the arm of S25 at station 3,

is not correct. The lamp may glow faintly, but it is not

contact 1-2 of S26, the loudspeaker, contact 4-5 of S26,

important. The polarity test checks the polarity of the

terminals Y4 and Y3, contact 5-6 of K1, terminal Y2

line and signal voltage windings (terminals 10-11 and

over line MC3Y21 to terminal Y1 of station 3A,

8-9, respectively) of the power transformer, T3.

terminal 7 of T2, the arm of S25, contact 1-2 of S26, the

loudspeaker, contact 4-5 of S26, to terminals Y4-Y3,

Call Lamp Test

contact 5-6 of K1, terminal Y2, over line MC3Y12,

terminal Y 1 in station 3, to complete the circuit at

To test the call lamp of the unit, operate call lamp

terminal 7 of T2.

test switch S212 on the test fixture. Call lamp 12 on the

unit under test should be lighted.

The volume at both stations will be the same and

can be controlled by either volume control S25. Both

Amplifier and Reproducer Test

volume controls, however, should be kept at the same

setting.

To test the amplifier and reproducer, depress the talk

If talk relay K1 is operated at either station, the input

switch microphone and talk into the microphone. The

to the audio circuit will be open for both stations.

talker should hear his/her voice clearly through the

reproducer. Rotate volume control knob S25 on the unit

under test while talking into the microphone, and

MAINTENANCE

observe the effect on the output volume. Now place the

microphone close to the reproducer. A microphone

A test fixture is provided with the maintenance parts

feedback should be observed when the volume control

of the equipment to facilitate testing the intercom units.

is in the full-volume position as well as at one step below

The test fixture is housed in a metal case and includes

full volume. This test provides a rough indication of the

the necessary switches, resistors, and controls to

amplifier gain, power output, and the general

perform all essential tests on a unit. It is provided with

performance of the entire unit, except for the signaling

a line cord and plug for connection to the ship's 115-volt,

circuits.

60-Hz power supply, and suitable female connectors for

attaching it to the rear of the unit under test. The front

Station Selector Circuit Test

cover contains 11 double-pole, double-throw (DPDT)

test switches, S201 through S211, a single-pole,

On the test fixture (fig. 7-30), operate talk test

single-throw (SPST) call lamp test switch, S212, an

switch S213 to the TALK position with the microphone

SPST talk test switch, S213, a DPDT polarity test

reasonably close to the reproducer to produce a

switch, S214, and an indicator lamp, I201. A wiring

microphonics howl. Reduce the volume control to the

diagram of a test fixture is illustrated in figure 7-30.

minimum position at which the howl can still be

To use the test fixture, remove the intercom unit to

obtained by moving the microphone as close to the

reproducer as required. This position will produce the

be tested from its case. Attach the test fixture to the rear

minimum objectionable howl during the subsequent

of the unit by plugging it into the unit. Connect the line

cord and plug to the ship's 115-volt, 60-Hz power. On

station selector circuit tests.

the test fixture, operate talk switch S213 to the OFF

When test switch S201 is in the TEST position, it

position and the 11 test switches, S201 through S211, to

places a short circuit across terminal 1 and 1C to

the STANDBY position. On the unit under test, depress

interrupt the microphonics howl.

release push button S1, turn volume control S25 and

On the unit under test, depress station selector push

dimmer control S27 to the extreme clockwise positions,

button S2 (adjacent to release push button S1). On the

and connect a microphone or handset into microphone

test fixture, operate test switch S202 to the STANDBY

jack J6.

7-30