Replacement of Parts, Minor Components for Use with Tuning Units 2, 3, and 4

(d) Open or shorted circuit in the

f r o m the center conductor to the

signal

output red color-coded

w i p e r arm of switch section

connector J1101 (fig. 81). Check

S1001B. Also check for infinite re-

f o r continuity from the center

s i s t a n c e between the center con-

c o n d u c t o r to the wiper arm of

ductor of J1001 and the outer shell.

switch

section S1101B. Also

If replacement of J1001 is re-

c h e c k for infinite resistance be-

quired, be sure to tag the lead

tween the center conductor of

connected from S1001B wiper arm

J1101 and the outer shell. If re-

t o J1001, before unsoldering, to

p l a c e m e n t of J1101 is required,

f a c i l i t a t e proper rewiring.

be sure to tag the lead connected

from S1101B wiper arm to Jll0l,

77. Replacement of Parts, Minor

b e f o r e unsoldering, to facilitate

Components for Use with Tuning

p r o p e r rewiring.

Units 2, 3, and 4

e. Loop Antenna AT-l026/URM-85 (fig.

a. General. After completing the tests

83). Disconnect the signal generator from

outlined in paragraphs 72 through 74, the

the test setup (fig. 79), and use the method

c h e c k i n g performance of this minor com-

s i g n a l substitution technique can be used

ponent as outlined in paragraph 43b, steps

f o r determining whether parts within the

70 through 72, TM 11-6625-351-12. If trou-

m i n o r components supplied for use with

ble is encountered in testing anyone of the

tuning units 2, 3, and 4 require repair or

six bands, refer to the schematic diagram

r e p l a c e m e n t . These tests are performed

with the applicable tuning unit installed in

(fig. 36) and to the exploded view (fig. 83).

Avoid unnecessary disassembly; follow the

t h e tuning unit compartment of the main

exploded view and disassemble only to the

unit. Similar to the procedure outlined in

e x t e n t necessary to correct the trouble.

p a r a g r a p h 7 la, the following procedures

P o s s i b l e sources of trouble are:

a r e based on the assumption that sources

(1) O p e n or shorted ferrite core step-

of trouble in the installed tuning unit and

t h e main unit- have been eliminated. All

up transformers T1001 through

t e s t s use Cable Assembly Set, Electrical

T1004, mounted on terminal board

MX-3410/URM-85 as the means of coupling

TB1001.

the test signal from the output of the minor

(2) B a n d switch S1001 fails to make

c o m p o n e n t under test to front-panel SIG

c o n t a c t in any or all of the six

NAL INPUT jack (J705). It is only neces-

p o s i t i o n s . In bands 5 and 6 (fig.

sary to test the performance of the minor

3 6 ) , no coupling transformer is

component with either tuning unit 2, 3, or

u s e d . If trouble is encountered in

4 installed in the main unit. For conven-

either of these bands, suspect faulty

ience, the 20- to 70-mc band of tuning unit

contacts 5 and 6, and the wiper on

2 is used throughout the following pro-

section C of S1001.

c e d u r e s . Set the front-panel controls as

(3) O p e n circuit in the impulse gen-

listed in paragraph 72a; monitor the output

e r a t o r injection network, consist-

signal by observing the pointer deflection

i n g of series resistor R1001 and

on the main unit panel meter. If desired,

shunt resistor R1002 (fig. 36). Do

simultaneously monitor the modulated test

not attempt to replace the individual

signal with the headset. Use tuning unit 4

r e s i s t o r s , s i n c e they are housed

signal generator as the signal source, with

and inaccessible w i t h i n green

1,000-cps modulation, and proceed as in-

color-coded connector assembly

dicated in b below.

J1002; if trouble is isolated to this

b. Coupler, Radio Frequency Interfer-

c i r c u i t, replace the entire con-

e n c e CU-897/URM-85 (fig. 38 and 84). In

n e c t o r assembly.

the test setup of figure 79, replace tuning

(4) Open or shorted circuit in the sig-

unit 1 signal generator with tuning unit 4

n a l output red color-coded con-

s i g n a l generator. Use an alligator clip to

nector J1001. Check for continuity

172