Signal Substitution, Tuning Unit 1

note is not heard in the headset, trouble is

Control

Setting

i n d i c a t e d . Connect the tuning unit to the

main unit through the test harness so that

MEGACYCLES ban

Band 1 (0.15 -- 0.36) or

the test points will be accessible.

switch.

band 3 (0.87 -- 2.1) mc.

Calibration switch ------

SERIES CAL & OPERATE.

N o t e : As the test connection point is changed

IMPULSE GENERATOR

OFF.

when working back from the final output to earlier

DB ABOVE lV/MC

input stages, reduce the level of the signal from

switch,

the signal generator. Also, rotate the GAIN control

POWER switch - - - - - - - -

ON.

counterclockwise from ita original midposition set-

GAIN control

Originally at midposition;

t i n g so that the pointer on the main unit panel-

then rotated counterclock-

mounted meter maintains an onscale indication. At

wise as additional ampli-

s o m e frequency points, it may be necessary to ro-

fiers are inserted in signal

tate the SIGNAL ATTENUATOR DB switch from

path.

its originally suggested setting of 20 (in the charts

VOLUME control

Set for comfortable level of

below) to higher attenuation factors of 40, 60, or

audio signal from headset.

80 db. Higher steps of attenuation in the path of

the output from the signal generator will have no

effect on the signal substitution technique of trou-

b. Check of 455-Kc and 1,600-Kc If. Am-

b l e s h o o t i n g as long as an onscale meter pointer

d e f l e c t i o n is maintained throughout the following

p l i f i e r . The 455-kc if. amplifier (fig. 62)

procedures.

i s energized only when MEGACYCLES

band switch S1 is rotated to band 1 (0.15 -

71. Signal Substitution, Tuning Unit 1

0.36) and band 3 (0.87 2.1). In addition,

t h e heterodyned output of the rf tuner

section is provided with a path of continuity

a. If. Chart. Use the tuning unit 1 signal

through the if. input selector, the if. step

generator (para 65), with 400-cps modula-

tion. Allow tuning unit 1, the main unit,

attenuator, the 455-kc if. amplifier, and the

and the tuning unit 1 signal generator to

if. output selector only when switch S1 is

warm up for at least 1/2 hour before start-

in bands 1 and 3. First check the 455-kc

ing the tests. Set the front-panel controls

i f . amplifier; then rotate the band switch

on the test set as follows:

to band 2, 4, 5, or 6. This action deener-

g i z e s the 455-kc if. amplifier, energizes

Setting

t h e 1,600-kc if. amplifier (fig. 61), and

Control

p r o v i d e s a different signal path through

CW AVERAGE.

Function switch - - - - - - -

t h e tuning unit for the output of mixer

SIGNAL ATTENUATOR

20.

stage V2.

DB switch.

Signal

frequency

Connection to

Possible trouble

(kc)

Defective headset or headset cord, audio

Input jack J5 on if. output selector (fig. 63).

455

amplifier in main unit, detector and electro-

Disconnect plug P6 (fig. 56) from mating

meter assembly A1, or if. output selector;

jack J5 and inject signal from external sig-

nal generator.

or open circuit at terminals of multipin

connector P1, P9 mating A1J2, or P7

mating A1J1. If above circuit points check

out satisfactorily, trouble is localized to if.

output selector. Isolate trouble as outlined

in troubleshooting chart (para 67).

V11 fourth if. amplifier plate pin 5 ------------

455

Defective or misaligned T34 network or ter-

mination CP4; open C166, R86, or R87; or

Caution: Reconnect plug P6 to mating jack

shorted C163 or C164.

J5 on if. output seletor before starting this

test.

V11 fourth if. amplifier grid, pin 1. -----------

455

Defective V11; open R83, R84, or shorted

C158 or C161.

V10 third if. amplifier plate, pin 5. ------------

Defective or misaligned T33 network; open

455

R62; or shorted C155.

V10 third if, amplifier grid, pin 1 -----------

Defective V10; open R77 or R78; or shorted

455

C152, C154.

V9 third if. amplifier plate, pin 5 ----------

455

Defective or misaligned T32 network; open

R76; or shorted C 148.

155