Replacement of Parts, Tuning Units

80. Replacement of Parts, Tuning Units

d. Replacement of Parts in Filter Box

Note: Several parts used in the tuning units have

for Con n e c t or J701, Rear of Main Unit

smaller tolrances than those that those used in most radio

(fig. 51). The parts mounted within the fil-

e q u i p m e n t . All resistors which are part of the if.

t e r box function to decouple rf and if.

step attenuators are precision 1 percent tolerance

currents from entering the various ac and

parts. F o r tuning unit 1 if. step attenuator AT1,

these parts are R33 through R37; for tuning unit 2,

d c outputs developed by the main unit

they are AT201R1 through AT201R5; for tuning unit

power supplies. The decoupling com-

3, they are AT401R1 through AT401T5; for tuning

p o n e n t s consist of 1,000-uuf feedthrough

unit 4, they are AT501R1 through AT501R5. I f

b y p a s s capacitors (C741 through C758),

these parts require replacement, use the ewzct val-

ue of the part removed. I f even slightly different

and 7-microhenry series-connected rf

values are used, the accuracy of the test set will

chokes (L701 through 1.716 and L718). Each

be affected.

c h o k e is enclosed in a green insulated

a. Tuning Unit 1. The m a j o r sub-

c o a t i n g . If these parts r e qu i r e re-

a s s e m b l i e s within tuning unit 1, working

placement, use only an identical item for

clockwise from the top center of figure 56,

t h e part removed. Refer to figure 45 for

consist of the items listed in the chart that

the reference symbol identification and for

follows. Identification of the parts within

t y p i c a l voltage and resistance values that

e a c h subassembly can be determined by

should exist at the terminals of the feed-

r e f e r r i n g to the individual illustration of

t h r o u g h capacitors. Failure to obtain cor-

the subassembly. Follow the exploded view

r e s p o n d e n c e between a measured value

i l l u s t r a t i o n for removal and reassembly

a n d that indicated in figure 45 requires

p r o c e d u r e s of a defective subassembly.

troubleshooting and replacement of the de-

A v o i d unnecessary disassembly; dis-

f e c t i v e part or parts.

a s s e m b l e only to the extent necessary to

e. D is a s s e m b l y and Replacement of

r e p l a c e or repair the defective part.

O t h e r Parts. D i s a s s e m b l y and re-

placement of other parts in the main unit

are obvious from the exploded view illus-

Subasseembly

Detailed identification of parte

trations. The following chart identifies the

f i g u r e number and the major subassem-

Rf tuner

Top side of rf tuner chassis shown

chassis.

in upper right corner of figure 56;

blies shown on the applicable illustration.

parts mounted on bottom side

shown in figure 57,

parts mounted within subassembly

If. input

Major parts and subassemblies

Figure

selector.

(fig. 59).

Six-position

Parts mounted on each of the six

turret tuner.

turret tamer segments (fig. 58).

Interior of front panel and parts mounted

1,600-kc if.

Parts mounted on wiring side (fig.

on top of chassis, voltage regulator as-

61) ,

amplifier.

sembly shown in position on uppar deck,

If. step at-

Parts mounted within subassembly

and filter box cover removed from rear

temmtor ATL

(fig. 60).

of chassis.

455-kc if. am-

Parts mounted on wiring side (fig.

Additional parts mounted on front panel

plifier.

62) .

and top of chassis; partition separating

IMtector and

Parts within sealed assembly are

upper deck from main deck exploded

electrometer

not separately replaceable; if

view for clarity; location of chassis ad-

aasembly Al

sealed unit is defective, discon-

justment controls R762, R776, R778,

nect multipfn plug I% from mat-

R789, S704, and S709; mounting phte

ing jack A1J2, on interior side of

for coaxial day K701 with right-angle

tuning unit 1 chassis. Remove the

adapter CP701; components mounted on

four screws and washers that se-

terminal boards TB701 and TB704.

cure sealed assembly to rear of

Parts mounted on function switch S702,

framework assembly; then gently

impulse generator coarse output level

pull entire sealed assembly

control S707, and impulse generator

straight back from the framework

fine output level control S708.

to disengage coaxial jack AIJ1

Parta mounted within perforated shield

from mating pl~ P7 (fig. 56) at

box of voltage regulator assembly, on

rear plate of if. output selector.

upper deck of main unit chassis.

Reassemble replacement sealed

Parts mounted on wiring side of chassis.

assembly in reverse order.

For detaila of components mounted on

If. Output

Parts mounted within subassembly

terminal boards TB702, TB703, TB705,

selector.

(fig. 63).

and TB706, see figure 43.

188