Audio Stage Gain on Receive

plifier, or the 3.0-3.9-mc if. subunits. Op-

100. Audio Stage Gain on Receive

erate Radio Set AN/VRC-24 or AN/TRC-

The voltage measurements listed in the

68 on normal receive. Check for proper

following chart will aid in locating a faulty

input voltages (para 100). Use Multimeter

stage or circuit component in the audio

ME-26/U to measure the voltages at the

amplifier and modulator subunit. Operate

test points listed. Voltages listed are for

Radio Set AN/VRC-24 or AN/TRC-68 on

frequencies in the range of 225.0 to 399.9

normal receive. Turn the SQUELCH con-

mc.

trol on the front panel to OFF. Use a vari-

able autotransformer and the ME-30/U to

obtain 115 (or 230) volts ac input to Radio

Voltage

(volts dc)

Check

Test point

Set AN/TRC-68, or use a potentiometer

and Multimeter ME-26/U to obtain 26.4

-0.8 to -1.7

V201

and associated

cir-

J201 (fig. 53)

volts dc input to Radio Set AN/VRC-24;

cuit

components.

+0. 38 to 0. 43 V202

and associated

cir-

J202 (fig. 53)

then, connect the audio test box (para 128)

cuit

components.

and the ME-30/U to either front panel

+0.8 to 1.1

V203

and associated

cir-

J203 (fig. 53)

AUDIO jack (fig. 38). Connect the volt-

cuit

components.

+1.1 to 2.1

V204

and associated

cir-

J204 (fig. 53)

meter leads and a 600-ohm load across

cuit

components.

the SPEAKER and AF OUTPUT RETURN

t e r m i n a l s . (Connect oscilloscope AN/

N o t e . If reading is 1.1 volts

at J203 and J204, trouble is

USM-50 across these terminals to check

indicated in V204.

for spurious noise voltages.) Use Audio

-0.94 to -3.8 V205 and associated cir-

J106 (fig. 68)

Oscillator TS-382/U and inject a 1,000-cps

cuit components, or

coaxial cable W4.

signal to the test points indicated in the

-2.0 to -2.6 V305 and associated cir-

J305 (fig. 62)

following chart. Adjust the audio voltage

cuit components.

level of the audio oscillator to obtain a

-7.0 to -12.0 V401 and associated cir-

J404 (fig. 56)

cuit components.

24.5-volt ac indication on the ME-30/U.

If the audio oscillator TS-382/U input re-

quired to obtain a 24.5 volt ac reading is

102. Transmitter Signal Tracing

greater than the input indicated in the fol-

(fig. 128)

lowing chart, ckeck the circuits and com-

Use the following chart to locate defec-

ponents indicated.

tive circuits or stages while the radio set

is operating on transmit. Before keying the

Audio voltage

t r a n s m i t t e r , connect R a d i o F r e q u e n c y

Check

Test point

level

(volts

dc)

Wattmeter AN/URM-43A to the ANT. jack

0.93

Audio output cir-

J802 (fig. 76).

on the front panel. Before measuring volt-

cuits, including

ages at the test points indicated, check the

V804, T801, V805,

V806, V807, V808,

input voltage to the radio set (para 100).

and T802 (fig. 14).

Use Multimeter ME-26/U to measure volt-

Audio input circuits

0.042

BROADBAND jack

ages. Voltages listed in the chart are for

to V803 and asso-

J704-A (NOR BB

ciated circuit com-

the frequency range from 225.0 to 399.9

switch S801 in

ponents (fig. 20).

BB position) (TM

mc.

11-5820-222-10).

Audio input circuits

2.3

J506 (fig. 59).

Voltage

to V804, includ-

Check

Test point

(volts dc)

ing S801 and K801.

V401 and third oscilla-

-6 to -12

J404 (fig. 56)

tor circuit components.

101. Receiver Signal Tracing

V401 or buffer amplifier

3 to 3.8

J402 (fig. 56)

(fig. 128)

circuit components.

Z403, Z402, and Z401

-0.3 to -0.98

J304 (fig. 62)

(fig. 56).

The voltage measurements listed in the

-1.4 to -2.6 V305 or associated cir-

J305 (fig. 62)

following chart will aid in locating a mal-

cuit components.

functioning stage or circuit component in

V304 or associated cir-

-1 to -1.5

J301 (fig. 62)

the uhf injection subunit, the first if. am-

cuit components.

127