TM 11-6625-441-34
CHAPTER 2
FUNCTIONING
2-1. Application, Block Diagram Analysis
a. The interphone test set is used to check the
serviceability of the interphone control. Block
diagram analysis of the interphone test is covered
in b below. Functioning of the receiving test
circuitry, transmission test circuitry, and self-
test circuitry is covered in paragraphs 2-2, 2-3,
and 2-4, respectively.
b. When using the interphone test set to check
an interphone control, five items of test equip-
ment are required to provide a complete test
setup: a power supply, an audio oscillator, an
output meter, a multimeter, and a headset.
microphone.
c. The test setup simulates input and output
Figure 2-1. Znterphone test set applicatwn, bluck diagmm.
signals and interconnections of the airborne
2-2. Receiving Test Circuit Functioning
intercommunications system in which the in-
terphone control is used. The audio oscillator
provides input and output signals to the in-
NOTE
terphone control through switching circuits of the
The receiving test circuitry of the in-
interphone test set. The audio input signals
terphone test set tests the nine receiver
received by the interphone control from the in-
circuits and interphone audio lines of the
terphone test set are similar to signals received
interphone control.
from a radio receiver. The output signals of the
a. Power to energize the interphone control is
audio oscillator can also be routed through the
provided by a 28-volt de power supply. The power
is applied through POWER-OFF switch S7 and 1
interphone test set to the interphone control to
simulate an audio input signal from a microphone
AMP FUSE F1. FUSE F1 provides over-current
protection for both the interphone test set and
for radio transmission or intercom distribution.
The interphone test set also simulates the
interphone control. O P E R A T E l a m p 1 1 i s
connected to the power supply circuit contacts D2
transmitter keying operation of a microphone
and D3 of relay K1 and goes on when POWER-
press-to-talk switch. A headset microphone may
OFF switch S7 is placed in the POWER position.
be used as a substitute for the audio oscillator and
b. An audio signal is applied to the interphone
the output meter for audio monitoring. The
control as a simulated radio receiver output from
output meter monitors the amplified audio output
the audio oscillator, and enters the interphone
power levels from the interphone control. The
test set at AUDIO OSC jacks J1 and J2. The
interphone test set switches select input and
signal is applied through contacts C2 and C3 of
output connections to the interphone control to
relay K1 to INPUT SEL switch S3. When testing
permit testing of each receiver, transmitter and
the receiver circuits of an interphone control,
interphone channel of the interphone control.
INPUT SEL switch S3 is placed in R (receive);
Included in the interphone test set is a built-in
the audio signal developed across load resistor R3
capability for self-testing of its internal circuitry.
is applied to the wiper contact of RECEIVER
The power supply provides 28 volts direct current
SEL switch S4.
(vdc) to the interphone test set and the interphone
control being tested. The multimeter monitors the
c. RECEIVER SEL switch S4 routes the audio
input voltage being applied to the interphone test
signal to the selected receiver channel of the
set by the power supply.
interphone control (positions 1 through 7, IN-
2-1
