Zenith J584W - Page 33

80 pages

Save Page as PDF

To Next Page

To Next Page

To Previous Page

To Previous Page

Loading...

Figure

17

is

a

schematic

of

the

1WJR55

IC

output

stage,

while

Figure

18

is

a

block

diagram

of

the

IC

with

external

compon



ents.

Signal

from

the

conventional

Loudness,

Tone

and

Bal



ance

controls

is

applied

to

the

circuit

shown,

to

be

coupled

I

to

pin

2

of

the

IC

via

C463.

Capacitors

C462

and

C465,

at

either

side

of

C463,

are

for

RFI

(audio

rectification)

suppres



sion.

In

addition

to

output

coupling

capacitor

C472

at

pin

13,

there

is

a

resistive

divider

consisting

of

R467

and

R468

which

are

part

of

the

feedback

loop,

determining

gain

of

the

chip.

C464

provides

de

decoupling

of

the

feedback

loop

to

pin

7.

Also

at

pin

13

are

C468

and

C469

which

provide

high

fre



quency

compensation

(roll

off)

for

higher

stability.

C471

and

R469

are

also

incorporated

to

prevent

possible

high

frequency

oscillation

that

could

occur

due

to

the

high

gain

of

this

chip.

C466

provides

additional

decoupling

for

the

chip.

R465

is

in

the

inputs

base

bias

circuit.

Several

precautions

must

be

noted

while

troubleshooting

or

servicing

this

chassis:

1.

Do

not

permit

output

pin

13

(or

its

foil

path)

to

be

shorted

to

either

B+

or

ground.

Shorting

pin

13

to

B+

or

ground

could

destroy

the

chip.

Ground

is

located

both

at

pin

14

on

one

side

of

pin

13

and

also

the

ground

tab

on

the

otherside

of

pin

13.

2.

When

replacing

a

IC,

be

certain

that

the

heat

sink

tabs

of

the

IC

(the

equivalent

of

pins

3,

4,

5,

10,

11

and

12)

are

completely

soldered

to

the

foil.

3.

Use

only

a

16

ohm

load.

To

use

a

smaller

load

(8

ohm)

could

cause

the

IC

to

overheat

and

be

destroyed.

POLARIZED

AC

PLUGS

"J"

Line"

Stereo

Chassis

3WJR50

and

15WJR29

(used

in

Modular,

Console

and

Color

Combination

models)

are

equipped

with

a

polarized

two

contact

AC

plug

of

the

general

type

illus



trated

in

Figure

19.

One

of

the

two

parallel

blades

is

of

a

distinctive

shape

and

is

wider

than

the

other

blade.

This

will

insure

that

the

plug

is

properly

inserted

into

a

two

contact

polarized

socket.

In

Chassis

3WJR50

power

supply

schematic

of

Figure

20,

the

lower

contact

of

the

plug

is

the

wide

blade

and

is

connected

to

the

common

return

of

the

chassis

AC

circuit.

It

also

has

a

very

high

value

resistor

RX502

between

AC

common

and

ground.

Using

a

plug

and

socket

combination

of

this

type

is

intended

to

minimize

hum

and

also

increase

consumer

and

product

safety.

Under

no

circumstances

should

anyone

attempt

to

defeat

the

plugs

design,

or

intent.

31