Marantz 2245 Manuale utente

SERVICE

MANUAL

model

2245

‘NBS

Fy

aS

ta

Vad

ats

Pats

a

ta

ra

Fags

BS

C4

7Y¥N

:

o

a

”

‘SPECIFICATIONS

Audio

Circuits:

Rated

continuous

(RMS)

power

output

per

channel,

both

channels

operating

simultaneously;

20

Hz

to

20,000

HZ

jaa

verse

ee

eee

eke

vee

eee

irene

ees

45

Watts

at

4

and

8

ohms

5

25

Watts

at

16

ohms

Compatable

Total

Music

Power

(IHF)

3

.c

3

cc

ew

erantetwen

nds

Gaeta

at

aewe

s

135

Watts

at

8

ohms

High-level

hum

and

noise

(ref.

4OW

at

Bohms)

...

16.

ee

cette

eee

—80

dB

Phono

hum

and

noise

2...

ee

en

eee

nent

teen

nnes

1.5

nV

equivalent

input

Dynamic

range

(phono

input

to

tape

recording

Output)

.

0...

eee

ete

nee

96

dB

i.

Me

Distortion

(SMPTE),.at

tated

POWEF.

a.

cae

ee

aoe

cae

es

we

ae

Oe

peewee

eed

ewes

0.3%

Distortion

decreases

as

output

is

lowered

Total

Harmonic

Distortion,

at

rated

poWer

«6.

cee

ee

eens

0.3%

Maximum

ue

~~

Distortion

decreases

as

output

is

lowered

wa.

ower

Bandwidth

(IHF)

for

0.3%

THD

2.0.0...

0.

ccc

eee

cece

e

ees

ene

serene

7

Hz

to

70,000

Hz

Damping

Factor

(ref.

8

OPTS)’.

<2

Soe

Sess

Nee

eS

akg

Sb

Seether

beter

oa

be

ala

Ree

Rawat

eh

Greater

than

45

Frequency

Response

Through

phono

ttt

tt

ttt

teen

ee

ene

eee

e

eee

+7dB

tnput

Sensitivity

(for

40W

at

8

ohms)

FIG

IOV.

|

wecck

Slaieicel

ooo

Se

les

a

eh

See

0

de

eeu

ets

Se

ae GR

Ea

ATE

Oe

IG

Ege

Sale

wegen

ieee

a

180

mV

Phono

T1000

HZ)

Aas

este

aetna

ey

et

i

eaters

Rach

ae

eae

aee

&

KS

aha

Aa

we

aa

1.8

mV

Input

|!mpedance

:

High-level

re

100,000

ohms

PHOMO

=

acdc

cook

ae

woke

PA

oe

en

eg

BIS

ek

nde

beat

peal

Taal

URE

se

gaseina

la

aia

ee

eee

kaka:

47,000

ohms

Channel

Separation

20

Hz

10:

20,000

HZ

5.

.ae

cree

raids

Beene

t

ae

ee

eg

dane

S

35

dB

Minimum

FM

Sections:

THE

Usable

Sensitwityes

Gat

so

aaee

626

ae

ade

ea

oe

oo

pe

ema

ete

Ma

hetie

argtaud

walneaee

ace

2.3

uV

SSFECEIVFEY?

atin.

wand

pas

ee

row

PO

Pe

ae

eee

ee

Ree

E

ROMA

ee

ta

ee

aee

ees

60

dB

INDISEQUTBEING

=o

vos

kor

ase

ae ak

wk

oe

er

a

ae

UN

oe

ts

i

Se

A

salt

arid

ea

veh

eieaea

~55

dB

at

5uV

eet

—60

dB

at

10uV

.

,

—65

dB

at

50ynV

Total

Harmonic

Distortion,

400

Hz,

100%

Mod.

.......

02...

cee

eee

(Mono)

0.2%

(Stereo)

0.4%

Frequency

Response

(ref.75u

sec.

deemphasis)

2.2...

0...

eee

ee

+1dB

50Hz

to

15KHz

Stereo

Separation

score

bi

ha

dee

ane

tesew

Sa

ee

ks

Ge

net

at

ele

Stew

4

1,000

Hz 40

dB

Sub-

Carrier

(38-kHz)

Suppression

sce.

sea

si

ae

eee

ee

se

ore

Hobs

pidlne

a

Seated

eaees

60

dB

General:

Power

Requirements

sc

vadie

sy

ete

eed

dua

eenree

ee

bee

ee

eton

be

hee

aes

100/17

20/200/220/240V

AC

~

50to

60

Hz

At

rated

output,

both

channels

operating

.........

0.0

cee

eee

e

eee

n

eee

ues

310

Watts

idling

Power

(Volume

Control

at

zero)

oo...

ec

ent

e

ee

nee

eens

nees

34

Watts

Dimensions

PARC

UAW

ors

aerate

velueuoue

Rin

use

Pe

tem

hg

ad

same

Mae

Ales

e

Ls

17

2"/g4

Inches

Panel

HEIN

24h

anv

washes

fire

tt

ate

ae

at

dt

pests,

Whar

ace

lanes

5

25/4,

Inches

SRO

RI

ti

Sake

once

ib

ME

a

Ne

5

oO

deat

Nanelgd

wu

eae

t

ee

uia

BAT

y

tandltras

14

Inches

Weight

ME

ANON

i

ail

ny

iG

Sa

on

ole

ich

dae

dis

cao

Chan

Akan

etait

Sto

ale

34.5|bs

Packed

for

shipment

3...

Py

dea

ese

At

Pact

Cece

e

ee

ess.

44.5ibs

*

These

speciticati

j

:

. . .

SE

SPECHNCATIONS

and

exte:

yr

designs

may

he

cnanged

for

improvement

without

advance

notice.

TABLE

OF

CONTENTS

SECTION

PAGE

IMtroduCtion

=

oc.

8

eccse

dcene

Vale

Od

LW

Sw,

BAG

aw

Mme

W

SEE

SES

Ree

Se

FEE

EE

eee

1

Service

Notes

..

0.0...

cece

eee

i

cdane

alta

UasSahoace

Meats

whe

ete

te

erdsal

qual

vata

gx

ht

1

AME

TUNG

Fete

ec

thee

Gee

fen

A

ae

Rea

E

adh

ee

eo

G

Saige

Saw

en

T

IVE

Thee

co

hhc

Oe

ated

ee

sec

nears

Medan

easel

ae

pat

De

REIS

NG

Ces

OR

A

ra

ae

Sed

dae

aes

-2

Phono

and

Tone

Amplifiers

..

0.0.0...

0.

cece

eee

enna

4

Power

Amplifier

si4

san

aoe

pba

eed

a

ss

ERR

ew

UE

Eee

oe

eae

he

5

Power

Protection

Circuit

©...

0...

ce

ee

eee

eens

5

Speaker

Protector

Relay

Circuit...

0...

0.

ee

te

tenes

5

Suggestions

for

Trouble

Shooting

of

Power

Amplifier

..........

Site

Mech

dhe

haMihitaiataanead

6

Voltage

Conversion...

0.0...

eee

ees

ng

aca

a

ah

erat

OE

RE

a

ow

RAD

HS

WS

6

Test

Equipment

Required

for

Servicing

©...

1...

cee

eee

ete

tenes

8

AM

Alignment

Procedure

...

0...

ee

ete

eee

9

FM

Alignment

Procedure

2.1.1...

cc

ene

teen

9

STEREO

Separation

Alignment

.........

dal

cuss

gusdiae

CNG

oyneeg,

a

vara

e

terete

AG

Sarat

tans

9

Muting

Circuit

Alignment

si.

5.0.

ees

ak

es

3

2

we

PRE

ee

wee

as

10

Audio

Adjustment

2.0.2.0...

cc

ee

en

ee

ene

10

Parts

Lest)

sa4

pact

tel

ot

avn

ate

ites

eas

eae

oe

Rete

ae

arate

ae,

fe

ala

aie

alta

ne

ete

21

SpeciHGatlONs

occ

¢.cee

eae

terse

Ske

Ss

eg

ee

BS

OOS

ate

eMac

ha

Xe

29

LIST

OF

ILLUSTRATIONS

FIGURE

PAGE

1.

Remove

the

Terminal

Cover

..

0.0...

ccc

eee

ee

6

2.

Voltage

Conversion

Chart

...............45

Rig

ate

a

gee

Wieriaha

tg

Yate

edo

aah

es

nea

Os

7

3.

Lissajou

Figure

on

Oscilloscope

..

0.6...

et

tte

ees

11

4.

Dial

Stringing

s

3.

sccicha

ae

diate

walls

or Oh

Mi

eae

Gn

ae

Dee

Eels

Bie

ag

ee

hee

11

5.

Front

Panel

Adjustment

and

Component

Locations

...........0

cece

eee

12

6.

Main

Chassis

Component

Locations

(Top

View)

.............0

000s

e

eee

Bec

Nghtits,

12

7.

Rear

Panel

Adjustment

and

Component

Locations

.......

6...

cece

cee

eee

es

13

8.

Main

Chassis

Component

Locations

(Bottom

View)

......

0...

cc

cece

ee

eee

13

9.

FM

Front

End

Assembly

P100

Component

Locations.

..........

0.0.00.

e

eee

14

10.

FM

IF

Amplifier

Assembly

P200

Component

Locations

................0..00005

14

11.

FM

Detector

Assembly

P500

Component

Locations

........

0.00:

cece

eee

ene

15

12.

MPX

Stereo

Decoding

Amplifier

Assembly

P300

Component

Locations............

15

13.

Muting

Control

Amplitier

Assembly

P550

Component

Locations

...............45

16

-

14.

AM

Tuner

Unit

Assembly

P150

Component

Locations

.........

0.0.0.0...

0b

eee

16

15.

Phono

Amplifier

Assembly

P700

Component

Locations

...................00005

17

16.

Tone

Amplifier

Assembly

P400

Component

Locations

...............

00.00.00

17

17.

Power

Amplifier

Assembly

P750

Component

Locations

...........0.

ee

cee

eee

18

18.

Regulated

Power

Supply

and

Protection

Relay

Circuit

Assembly

P800

Component

Locations

0.

eee

ees

19

19.

Loudness,

High

and

Low

Filter

and

Muting

Switch

Unit

Assembly

P600

Component

Locations

........

00.0.

eee

ee

eee

19

20.

Schematic

Diagram

©...

2.2

ee

ees

20

INTRODUCTION

This

service

manual

was

prepared

for

use

by

Authorized

Warranty

Stations

and

contains

service

information

for

Marantz

Model

2245

Stereophonic

Receiver.

Servicing

information

and

voltage

data

included

in

this

manual

are

intended

for

use

by

the

knowledgeable

and

experienced

technician

only.

All

instruction

should

be

read

carefully.

No

attempt

should

be

made

to

proceed

without

a

good

understanding

of

the

operation

in

the

receiver.

The

parts

list

furnish

information

by

which

replacement

part

may

be

ordered

from

the

Marantz

Company.

A

simple

description

is

included

for

parts

which

can

be

usually

be

obtained

through

local

suppliers.

1.

Service

Notes

As

can

be

seen

from

the

circuit

diagram

the

chassis

of

Model

2245

consists

of

the

following

units.

Each

unit

mounted

on

a

printed

circuit

board

is

described

within

the

square

enclosed

by

a

bold

dotted

line

on

the

circuit

diagram.

1.

FM

FrontEnd

1...

00.

ee

_

mounted

on

P.C.

Board,

P100

2.

FMIF

Amplifier

2...

0

ee

_...

mounted

on

P.C.

Board,

P200

3:

(PM

Detector

Gover

eee

Boe

ke

HA

ee

Dw

ks

mounted

on

P.C.

Board,

P500

4,

MPX

Stereo

Decoding

Amplifier

2...

00.

ee

eee

mounted

on

P.C.

Board,

P300

5.

Muting

Control

Amplifier...

--

6-6-0

ee

eee

ees

mounted

on

P.C.

Board,

P550

6

SAM

TunerUAit

o

4c8

Sida

we

ce

ae

Ge

We

eS

mounted

on

P.C.

Board,

P150

7.

Phone

Amphtier

..ccwe

Ge

eee

So eo

Rees

ssestan

as

ec

mounted

on

P.C.

Board,

P700°

8.

Tone

Amplifier

cts

tues

oad

ae

i

ahs

Bn ee

Oe

ee

mounted

on

P.C.

Board,

P400.

9.

Power

Amplifier

.

50.

eb

de

eee

mounted

on

P.C.

Board,

P750_

10.

Regulated

Power

Supply

and

Protection

Relay

Circuit...

.

mounted

on

P.C.

Board,

P800

11,

Loudness,

High

and

Low

Filter,

and

Muting

Switch

Unit

. . .

mounted

on

P.C.

Board,

P600

2;

AM

Tuner

All

components

except

Tuning

capacitor

and

ferrite

bar

antenna

are

mounted

on

a

printed

circuit

board

P.150.

The

AM

signals

induced

in

a

ferrite

bar

antenna

are

applied

to

the

base

of

RF

amplifier

transistor

H151

through

a

capacitor

of

C151

and

amplified

to

the

level

required

for

overcoming

the

conversion

noises,

thus

giving

good

S/N

performance.

The

tuned

circuits

inserted

in

both

out

and

input

circuit

of

the

RF

amplifier

assure

very

high

image

and

spurious

rejection

performance.

Thus

amplified

and

selected

AM

signals

are

then

applied

to

the

base

of

converter

transistor

H1i52

through

a

coupling

capacitor

C156.

While

the

local

oscillator

voltage

is

injected

to

the

emitter

of

H152

through

a

capacitor

C157.

Both

AM

signals

and

oscillating

voltage

are

mixed

at

the

base-emitter

junction

and

converted

into

455KHz

intermediate

frequency.

The

resulting

IF

signal

is

applied

to

the

first

IF

transformer

1153

consisting

of

one

ceramic

filter

and

two

tuned

circuits.

The

output

of.

L153

is

led

to

the

transistor

H153

which

in

turn

apply

its

output

to

the

transistor

of

H154.

The

fully

amplified

IF

output

is

then

applied

to

the

diode

H157

to

detect

audible

signal

through

the

detector

transformer

L154.

The

detected

audio

signal

is

filtered

and

amplified

and

the

final

audio

output

is

obtained

from

the

collector

of

H155

and

applied:

one

to

the

tape

out

jacks

through

monitor

‘switch

on

the

front

panel

and

the

other

to

the

function

rotary

switch,

Se:

:

The

DC

component

of

the

detected

1F

signal

is

used

as

a

AGC

voltage

to

control

emitter

current

of

H153

which

in

turn

control

the

bias

current

of

the

RF

amplifier

through

the

resistor

R179

and

R751.

A

part

of

IF

signal

output

is

also

applied

to

the

diode

H158

through

a

capacitor

C167

and

rectified

to

obtain

DC

current

for

energizing

the

AM

signa!

strength

meter

Mo01,

Suggestions

for

AM

Tuner

Trouble

Shooting

Check

for

broken

AM

bar

antenna,

to

tune

station

by

rotating

fly-wheel

tuning

knob

slowly

and

observe

the

AM

signal

strength

meter

whether

it

deflects

or

not.

If

the

signal

strength

meter

gives

a

deflection

at

several

frequencies

received,

no

failure

may

exist

in

the

stages

at

least

preceding

final

1F

transformer

L154.

a.oscilloscope

to

the

terminal

J162

or

J157

and

check

for

audio

signals

with

the

tuning

meter

deflected.

If

the

signal

strength

meter

does

not

deflect,

check

the

local

oscillator

circuit.

Normal

oscillating

voltage

at

the

hot

end

of

the

oscillator

tuning

capacitor

is

about

2

or

3

volts,

varying

with

tuning

capacitor

position.

When

measuring

oscillating

voltage

use

a

RF

VTVM,

no

circuit

tester

gives

correct

indication.

!f

the

local

oscillator

voltage

is

normal,

check

all

voltage

distribution

in

the

AM

circuits

by

using

a

DC

VTVM

and

compare

the

measured

values

with

those

given

in

the

schematic

diagram.

3.

FM

Tuner

The

FM

Tuner

section

of

Model

2245

is

divided

into

five

functional

blocks:

FM

Front

End,

IF

Amplifier,

Detector,

Muting

Contro!

and

MPX

Stereo

Decoding

Circuit.

,

FM

signals

induced

by

a

FM

antenna

are

led

to

FM

antenna

coil

L101

through

an

attenuator

switch

and

a

Balun

coil.

These

signals

are

then

applied

to

the

FET

RF

amplifier

which

in

turn

applies

its

output

to

the

Mixer

H102

through

the

double

tuned

high

selective

circuits.

The

FET

Mixer

convert

its

input

signal

into

10.7MHz

intermediate

frequency

and

amplifies

it

at

the

same

time.

The

H103

is

a

local

oscillator

and

its

output

is

injected

into

the

source

of

the

FET

Mixer,

the

injection

voltage

is

about

700mvV.

The

10,7MHz

front

end

output

is

led

to

the

amplifier

unit

through

a

coaxial

cable.

:

The

IF

amplifier

unit

consists

of

five

stages

of

1F

amplifier

and

one

stage

of

AGC

amplifier.

Six

pieces

of

ceramic

filters

are

also

used

to

obtain

high

selectivity

four

stages

of

symmetrical!

diode

‘limiters

are

also

employed

for

the

best

limitting

characteristics,

improved

capture

ratio

and

good

AM

suppression.

A

part

of

FM

Front

End

output

is

applied

to

the

AGC

amplifier

H206

and

rectified

its

output

is

fed

back

to

the

gate

of

FET

RF

amplifier

to

decrease

the

gain

with

increased

signal

strength.

The

IF

signal

sufficiently

amplified

through

every

stage

of

1F

amplifier

is

finally

applied

to

the

IC

limiter

on

the

Detector

Unit.

The

detected

audio

output

is

fed

to

the

buffer

amplifier

H502

and

its

buffered

output

is

led

to;

(a)

noise

amplifier

H551

through

resistor

R551

and

capacitor

C551,

(b)

Quad

Radial

Jacks

on

the

rear

panel

through

resistor

R564,

(c)

MPX

stereo

decoding

circuit

through

R563.

The

DC

current

caused

at

the

third

windings

of

the

discriminator

transformer

is

directly

applied

to

the

FM

center

tuning

meter.

}

‘ea

proportional

to

the

noise

components

in

the

audio

signals.

Audio

Muting

and

Stereo

mode

auto-selecting

circuit

The

muting

circuit

consisting

of

all

solid-state

electrical

switching

has

been

incorporated

in

the

Model

2245.

Three

inputs

control

the

muting

function.

The

first

is

signal

strength,

the

second

to

the

noise

condition

at

the

detector

and

the

third

is

derived

from

the

DC

component

of

the

detector

output.

These

inputs

are

properly

matrixed

and

gated

to

provide

muting

free

from

noise

and

transients.

The

first

input

of

DC

voltage

obtained

by

rectifing

a

part

of

IF

output

signal

from

the

H205

is

applied

to

the

base

of.

H306

and

turns

on

it,

if

the

1F

output

is

greater

than

predetermined

level

(muting

threshold

level).

When

the

H306

is

turned

on

the

H307

is

turned

off,

allowing

the

emitter-collector

resistance

increasing

and

the

collector

voltage

rises

about

9V.

The

increased

collector

voltage

increases

the

gate

bias

voltage

and

turns

on

the

switching

FET

H308,

decreasing

the

source-drain

resistance

to

near

zero

ohm

and

allowing

the

audio

signal

applied

to

the

source

to

flow

to

the

center

of

38KHz

switching

transformer

through

the

source-drain

path.

;

When

the

input

signal

is

lower

than

predetermined

level,

the

DC

output

obtained

is

small

and

can

not

turn

on

the

H306,

thus

the

H306

keeps

its

turn-off

state

and

this

makes

H307

turn

on,

decreasing

the

collector

voltage

and

turning

off

H308.

Thus

no

audio

signals

can

pass

through

the

FET.

This

is

the

fundamental

principle

of

the

muting

operation

but

for

more

elaborate

muting

.

operation

the

second

and

the

third

inputs

are

necessary.

The

second

input

is

used

to

protect

the

muting

operation

and

MPX

stereo

beacon

lamps

from

“misoperation

due

to

undesirable

noises.

The

high

frequency

noises

included

in

the

detected

audio

signals

are

separated.

by

a

small

capacitor

C551

and

amplified

by

the

noise

amplifier

transistor

H551

and

its

output

is

rectified

by

the

two

diodes.

The

rectified

DC

output

is

When

there

are

excessive

noises

in

the

audio

signals

such

as

obtained

with

a

station

incorrectly

~

tuned

in,

the

rectified

DC

output

turns

on

the

transistor

H522,

decreasing

the

emitter-collector

resistance

to

zero.

This

means

the

collector

of

H307

is

short-circuited

to

the

ground,

therefore

.

the

H308

is

turned

off

and

any

audio

signals

having

excessive

high

frequency

noises

can

not

go

through

the

FET’s

sourcedrain

path.

The

transistor

H303

connected

in

series

with

the

19KHz

pilot

signal

amplifier

transistor

H302

is

also

turned

off

(when

the

transistor

4522

or

H307

are

turned

on.)

and

no

current

flows

in

the

H302,

resulting

in

turning

off

the

stereo

beacon

lamps.

Thus

misoperation

due

to

undesirable

noises

is

also

avoided.

The

third

input

is

obtained

from

the

EM

discriminator

circuit.

The

DC

output

so

called

“gr

curve

is

applied

to

the

gate

of

H553

through

a

resistor

R523

and

deviding

network

(R565

&

R566).

The

DC

output

is

zero

with

a

station

correctly

tuned

in,

but

will

vary

from

negative

to

positive

values

or

vice

versa

when

the

tuning

point

is

deviated

toward

either

plus

or

minus

frequency

from

the

correct

tuning

frequency.

When

the

DC

output

is

increased

to

a

greater

level

than

that

of

predetermined,

the

increased

source

potential

of

H558

makes

the

transistor

H561

turn

on,

and

this

makes

the

H306

turn

off,

...

H307

turn

on,

....

H308

turn

off,

....

1303

turn

off

(this

means

no

19KHz

pilot

signal

is

amplified

and

no

stereo

beacon

is

turned

on.)

When

the

DC

output

is

increased

to

the

negative

predetermined

level,

the

decreased

source

potential

turns

off

the

H559

which

in

turn

makes

the

4560

turn

on

and

the

H306

is

turned

off.

The

subsequent

changes

are

exactly

the

same

as

that

just

described

above.

Thus

when

the

tuning

is

shifted

or

deviated

to

the

certain

frequencies

in

which

undesirable

noisy

side-audio

signals

are

produced,

both

muting

and

19KHz

switching

transistors

are

operated

automatically

and

open

the

circuits.

-

oa

ae

With

the

station

correctly

tuned

in,

the

bias

current

of

the

FET

H558

is

adjusted

so

that

both

transistor

H560

and

H561

are

not

turned

on,

giving

no

effect

on

the

transistor

H306.

MPX

Stereo

Decoding

Circuit

The

buffered

and

non-equalized

audio

signals

are

applied

to

the

first

amplifier

H301

which

serves

as

a

tuned

amplifier

for

the

pilot

signal

in

the

composite

signals

and

as

a

buffer

amplifier

for

the

audio

signals.

The

amplified

19KHz

pilot

signal

is

led

to

the

second

19KHz

amplifier

H302

and

further

amplified

if

switching

transistor

H303

in

turned

on

by

the

controlling

BC

signal

as

described

in

the

preceding

chapter.

The

final

19KHz

pilot

signal

is

rectified

by

the

doubler

circuit

consisting

of

the

H315

and

H316

to

obtain

synchronized

38KHz

amplifier

driving

signal.

The

H304

is

the

38KHz

tuned

amplifier

and

supplies

its

output

to

the

switching

matrix

circuit

consisting

of

four

diodes.

While

the

composite

signals

are

applied

to

the

center

tap

of

switching

transformer

1/2

L302.

The

right

and

left

stereo

signals

decoded

by

the

switching

circuit

are

led

to

the

crosstalk

cancelling

amplifier

which

utilizes

complementary

configuration

with

NPN

and

PNP

transistors

through

de-emphasis

network

consisting

of

C315

and

R335,

and

C316

and

R336.

L305

is

a

low-pass

filter

networks

having

very

sharp

cut

off

characteristics

and

eliminates

undesirable

residual

switching

signals.

Transistors

H313

and

H314

are

buffer

amplifiers

and

their

outputs

are

led

to

the

function

switch.

Suggestion

for

Trouble

Shooting

of

FM

Tuner

Symptom:

No

FM

Reception

First

turn

on

the

power

switch

and

try

to

tune

FM

stations.

Rotate

the

fly-wheel

tuning

knob

slowly

and

observe

the

FM

signal

strength

meter

and

FM

center

tuning

meter.

|f

the

center

tuning

meter

deflect

at

several

frequencies

received,

the

tuner

circuits

preceding

the

discriminator

circuit

may

have

no

failure.

|f

the

signal

strength

meter

deflect

but

no

deflection

is

obtained

on

the

center

meter,

there

may

be

sore

defects

around

the

detecting

circuit

consisting

H501,

L501,

H503,

H504,

etc.

When

no

reading

is

obtained

in

both

meters,

check

FM

local

oscillator

circuit,

using

a

RF

VTVM.

The

normal

tocal

oscillator

voltage

is

one

or

two

volts

(rms)

at

the

tuning

capacitor,

depending

on

the

tuning

capacitor

positon.

If

the

local

oscillator

voltage

is

normal,

all

voltage

distribution

in

the

FM

Front

End

and

!F

amplifier

unit

and

compare

them

with

those

shown

in

the

circuit

ciagram.

When

both

meters

deflect

but

no

sound

is

obtained,

check

audio

circuits,

using

high

sensitive

oscilloscope.

Symptom:

No

Stereo

Separation:

First

check

the

MONO

switch

is

in

normal

out

position.

Connect

a

FM

RF

signal

generator

output

modulated

by.

a

stereo

modulator

to

the

rear

FM

antenna

terminals,

and

check

the

stereo

beacon

is

turned

on

or.not.

If

not

turned

on,

check

for

19KHz

pilot

signal

and

38KHz

switching

signal,

using

an

oscilloscope.

:

4,

Phono

and

Tone

Amplifiers

Program

source

signals

from

the

PHONO

jacks

on

the

rear

panel

are

supplied

to

the

input

circuit

of

the

Phono

Amplifier

through

the

selector

switch

and

the

output

of

the

Phono

Amplifier

is

applied

to

another

section

of

the

selector

switch.

This

amplifier

provides

a

gain

of

40dB.

All

signals

selected

by

the

funetion

switch

(S002-3F,

4F)

are

led

to

the

balance

and

volume

controls

through

the

MONO

switch.

Signals

.properly

attenuated

by

the

volume

control

are

applied

to

the

tone

amplifier

and

subjected

to

the

tone

control

networks

such

as

bass,

mid,

treble

control

and

high

and

fow

cut

filters.

Thus

controlled

audio

signals

are

then

led

to

the

PRE

OUT

jacks

on

the

rear

panel.

5.

Power

Amplifier

The

signal

from

the

tone

amplifier

is

applied

to

the

differential

amplifier

(base

of

H751)

through

the

coupling

capacitor

C751.

The

differential

amplifier

provides

very

high

input

impedance

and

its

collector

output

(H752)

is

applied

to

the

base

of

H753

which

in

turn

applies

its

Output

to

the

H756

through

the

network

R766,

C762

and

R771,

and

to

the

H757

through

the

network

R776,

C763

and

R772.

The

outputs-of

H756

and

H757

are

applied

to

the

H758

and

H757

respectively.

HOO1

and

HOO2

are

power

transistors

used

in

complementary

symmetry

configulation

and

mounted

on

the

heat

sink.

To

maintain

overall

amplifier

stability

and

linearity,

degenerative

feed

back

is

utilized

throughout

the

amplifier.

This

feed

back

is

also

necessary

to

reduce

distortion

to

within

specified

limit.

The

RC

network

R775

and

C756

condition

the

feed

back

signal

for

the

audio

signals.

R759

and

C755

are

also

a

feed

back

loop

provided

to

obtain

a

stable

zero

DC

off

set

voltage

at

tne

speaker

output

terminals.

The

R762

is

a

trimming

resistor

to

adjust

the

DC

off

set

voltage.

Dynamic

bias

is

applied

to

the

base

of

driver

transistors

H758

and

H757.

This

dynamic

bias

circuit

is

comprised

of

H761,

H760

and

R763.

This

provides

a

variable

base

bias

for

driver

transistors

that

automatically

maintains

the

proper

base

voltage

with

temperature

change.

The

ternperature

sensitive

biasing

components

of

the

dynamic

circuit

are

thermally

couppled

through

a

heatsink

to

the

power

amplifier

transistors.

6.

Power

Protection

Circuit

Protection

circuit

for

the

amplifier

is

provided

by

sensing

resistor

networks

and

two

switching

_

transistors.

When

the

output

transistors

are

over-driven,

the

current

increase

through

the

power

-

output

transistor

causes

an

increased

current

flow

through

R789

(or

R788)

and

the

potential

“across

the

R789

will

be

increased.

This

increased

voltage

potential

is

applied

to

the

base

of

H755

~

through

the

resistor

R783

and

turns

on

the

H755.

Since

the

collector

of

H755

is

directly

connected

to

the

base

of

H757,

this

means

that

the

base

of

H757

is

bypassed

to

the

ground

through

emitter-collector

path

of

H755.

Thus

the

input

signal

to

the

H757

is

restricted

to

the

value

which

maintains

the

operation

of

power

transistor

with

in

the

safety

area.

A

resistor

network

R777

and

R781

also

works

as

a

sensing

network.

When

the

center

voltage

(collector

voltage

of

power

transistors)

is

excessively

increased

to

a

positive

value

by

certain

troubles,

the

voltage

applied

to

the

base

of

H755

makes

the

H755

turn

on,

making

bypass

circuit,

and

protects

the

power

transistor.

For

the

other

half

cycle

of

driving

signal,

the

eperatig

principle

is

applied

provided.

7.

Speaker

Protector

Relay

Circuit

The

speaker

protection

circuit

consisting

of

H808,

H809,

H810,

etc

protects

the

speaker

systems

against

any

loud

“‘pop’’

sound

developed.

This

circuit

is

so

designed

that

no

sound

is

heard

for

the

first

three

or

five

seconds

after

the

power

switch

is

turned

on

by

the

time

constant

circuit

consisting

of

C807

and

R816.

This

circuit

also

protects

the

speaker

systems

against

some

troubles

due

to

DC

off

balance

between

the

speaker

system

terminals

by

instantly

operating

the

relay

and

cut

off

the

speaker

systems

from

the

circuit.

When

DC

off

balance

voltage

(positive)

is

developed

between

speaker

terminals

by

possible

defects

such

as

broken

power

transistor,

short-circuits,

or

broken

potentio

meter

R762,

as

the

base

of

H808

is

connected

to

the

speaker

terminal,

the

transistor

H808

is

turned

on

by

this

offset

voltage

developed

and

this

makes

the

transistor

H809

and

H810

turns

off,

thus

cutting

off

the

relay

and

disconnecting

the

speaker

from

the

output

circuit.

When

negative

offset

voltage

is

developed,

this

voltage

directly

turns

off

the

H809

and

H810,

thus

speaker

is

cut

off

from

the

circuit

and

protected.

Thecircuit

also

protects

the

speaker

systems

from

the

possible

damage

when

the

amplifier

is

aver-driven

by

very

bow

frequencies

such

as

7

or

Rad

cycles.

8.

Suggestions

for

Trouble

Shooting

of

Power

Amplifier

8.1

Excessive

Line

Consumption

3.

Check

for

shorted

rectifiers

HOO5;

also

check

C007

and

CO08.

b.

Check

for

shorted

transistors

H758

and

H759,

HOO1

and

HO02,

or

check

H760.

Check

for

open

control.

R763,

and

bias

diode

H761.

Check

L004

for

short.

CAUTION:

BECAUSE

THE

DRIVER

AND

OUTPUT

STAGES

ARE

DIRECT

COUPLED

COMPONENTS

MAY

FAIL

AS

A

DIRECT

RESULT

OF

AN

INITIAL

COM-

PONENT

FAILURE.

IF

A

SHORTED

TRANSISTOR

OR

ZENER

DIODE

IS

FOUND,

OR

CONTROL

OR

BIAS

DIODE,

BE

SURE

TO

CHECK

THE

REMAINING

DRIVER

AND

OUTPUT

COMPONENTS

FOR

SHORT

OR

OPEN

CIRCUIT

BEFORE

RE-ENERGIZING

THE

AMPLIFIER.

8.2

No

Line

Consumption

or

Zero

Bias

a.

Check

line

cord,

fuse,

transistors

H760, HOO1,

HOO2.

HOO3

and

HOO4,

bias

diode

H761.

b.

Check

for

open

rectifier

HOOS,

or

open

L004.

8.3

No

DC

Balance

3.

Check

R762

and

Zener

diodes

H762

and

H7/63.

9.

Voltage

Conversion

This

model

is

equipped

with

a

universal

power

transformer

to

permit

operation

at

100,

120,

200,

220

and.240V.

AC

50

to

60Hz.

To

convert

the

Model

2245

to

the

required

voltage

perform

the

following

steps:

(1)

Remove

the

top

cover.

(2)

Remove

the

Transformer

Wire

Connection

Terminal

Cover,

loosen

two

Cover

mounting

‘screws

on

the

rear

panel,

see

Fig.

1.

(3)

Change

the

jumper

wires

as

illustrated

in

Fig.

2

for

the

required

AC

voltage

and

replace

the

fuse

as

instructed.

CAUTION:

DISCONNECT

POWER

SUPPLY

CORD

FROM

AC

OUTLET

BEFORE

CONVERT-

ING

VOLTAGE.

REMOVE

SCREW

ene

aan

.

ea

je

&|

bs

—*

Be

»REMOVE

THIS

COVER

_

Figure

1.

‘Remove

the

Terminal

Cover

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