Jvc M-7050 User manual

JVC

Instruction

Book

&

Service

Manual

STEREO

POWER

AMPLIFIER

M-7050

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WARNING:

TO

PREVENT

FIRE

OR

SHOCK

HAZARD,

DO

NOT

EXPOSE

THIS

APPLIANCE

TO

RAIN

OR

MOISTURE.

For

Customer

Use:

Enter

below

the

Model

No.

and

Serial

No.

which

is

located

either

on

the

rear

or

bottom

of

the

cabinet.

Retain

this

information

for

future

reference.

Model

No.

Serial

No.

Service

manual

No.

2469

July,

1979

E30580-804A

IMPORTANT

(In

the

United

Kingdom)

Mains

Supply

(AC

240

V~,

50

Hz

only)

IMPORTANT

Do

not

make

any

connection

to

the

Larger

Terminal

coded

E

or

Green.

The

wires

in

the

mains

lead

are

coloured

in

accordance

with

following

code:

Blue

to

N

(Neutral)

of

Black

Brown

to

L

(Live)

or

Red

\f

these

colours

do

not

correspond

with

the

terminal

identifi-

cations

of

your

plug,

connect

as

follows:

Blue

wire

to

terminal

coded

N

(Neutral)

or

coloured

Black.

Brown

wire

to

terminal

coded

L

(Live)

or

coloured

Red.

If

in

doubt

—

consult

a

competent

electrician.

Note

We

recommend

that

you

should

disconnect

the

AC

cord

from

the

outlet.

INTRODUCTION

Thank

you

for

purchasing

the

JVC

M-7050

stereo

Power

Amplifier.

You

are

now

the

owner

of

a

truly

sophisti-

cated

system

component

incorporating

many

advanced

features.

“Super-A”

high

efficient

150W

+

150W

power

output

stage

(is

equal

to

class

B

operation)

of

extra

low

distortion

(is

superior

to

class

A

operation),

high

slew

rate

(+300V/ysec),

un-

rnesurerable

TIM

distortion,

non

magnetic

alminium

chassis-

base

to

eliminate

the

magnetostriction,

and

high

capacitive

power

supply

are

just

a

few

of

the

host

of

features

which

combine

to

produce

the

best

possible

sound.

JVC

also

manufactures

the

EQ—7070

Stereo

Phono

Equalizer,

a

matching

preamplifier

and

the

SEA—7070

Stereo

Graphic

Equalizer,

a

matching

frequency

characteristic

controller

for

use

with

the

M—7050

Power

Amplifier.

Before

you

begin

using,

please

read

the

instructions

carefully

to

be

sure

of

getting

the

best

possible

performance

from

the

new

unit.

Wishing

you

memorably

enjoyable

listening.

WARNING

Dangerous

voltage

inside

CAUTION

(

To

prevent

electric

shock,

do

not

remove

screws,

covers

or

cabinet.

No

user-serviceable

parts

inside.

Refer

servicing

to

qualified

service

personnel.

CONTENTS

Instruction

Manual

page

Front.panel.):.:

si.

eh

a

ee

FA

ee

g

Important

notes

2...

ee

5

Troubleshooting...

0.0.0.0...

eee

tee

ee

eee

6

Block

diagram.

6.2...

eee

ee

7

Performance

graphs...

2...

ee

es

8

Technical

description...

0...

ee

9

Specification

©...

6.

ee

et

ee

ees

10

Precautions

in

servicing

Adjustment

procedure

of

the

amplifier

Check

after

servicing

Exploded

views

Parts

list

of

exploded

views

Location

of

circuit

boards

Schematic

Diagram

(For

only

qualified

service

personnel)

cto,

et,

Instruction

Manual

FRONT

PANEL

PHONES

POWER

Switch

Headphones

jack

(PHONES)

Exclusively

for

monitoring

purposes.

Employ

this

facility

in

the

following

cases,

for

example:

1.

To

locate’the

beginning

of

a

particular

section

of

tape

when

no

speaker

sound

is

desirable.

2.

To

monitor

the

sound

to

be

transmitted

to

a

remote

place

when

the

amplifier

is

used

as

a

public

address

system.

(Note)

Plugging

in

the

headphones

does

not

switch

off

the

speaker

sound

automatically.

When

you

wish

to

listen

to

sound

from

the

headphones

only,

set

the

SPEAKER

switches

to

OFF.

POWER

switch

Press

to

turn

the

power

on.

The

red

indicator

lamp

in

push

knob

will

light

and

the

POWER

meters

will

be

illuminated.

To

turn

the

power

off,

press

the

switch

again

to

release.

Panel

IImination:

For

a

period

immediately

after

the

POWER

switch

is

turned

ON,

the

illumination

of

the

POWER

meters

is

red.

Wait

for

about

4

-

5

seconds

until

it

changes

to

white.

If

it

continues

to

be

red

for

a

longer

span,

the

protection

circuit

is

operating

for

some

reason.

Turn

the

POWER

switch

OFF

and

check

the

cause

of

malfunctioning.

——

Power

meter

SPEAKER

Switch

POWER

meters

The

output

power

is

indicated

in

wattage

on

the

compressed

logarithmic

scale

in

reference

to

the

8-ohm

load

impedance.

SPEAKER

switches

To

listen

to

the

speaker

system

connected

to

the

rear

panel

SYSTEM-1

terminals,

press

the

SYSTEM-1

switch.

To

listen

to

the

speaker

system

connected

to

the

rear

panel

SYSTEM-2

terminals,

press

the

SYSTEM-2

switch..

Both

speaker

systems

can

be

heard

by

pressing

both

switches.

When

a

SPEAKER

switch

is

pressed,

the

green

indicator

lamp

on

the

corresponding

switch

lights.

(Note)

If

the

load

impedance

is

lower

than

4

ohms,

the

protection

circuit

is

activated,

resulting

in

inter-

mittent

sound.

1.

If

a

single

pair

of

speakers

is

to

be

driven

at

a

time,

the

speaker

impedance

may

be

between

4

and

16

ohms.

2.

If

two

pairs

of

speakers

are

to

be

driven

simultaneously,

the

speaker

impedance

should

be

between

8

and

16

ohms.

CONNECTION

DIAGRAM

Refer

to

item

No.

3

in

page

5

Speaker

system

4

~

1622

Input

LEVEL

volume

Normally,

set

to

the

“MAX”

position.

If

the

preamplifier

produces

an

excessively

large’’

gain,

turn

the

control

counter-

clockwise

until

the

proper

adjustment

is

obtained.

Refer

to

item

No.

1

in

page

5

Refer

to

item

No.

2

in

page

5

Speaker

system

4

~

1692

SEA-7070

Graphic

equalizer

Pre-amplifier

Turn

table

Tape

Deck

a

IMPORTANT

one,

——

eeen

eoeow

Installation

Select

a

dry,

level

place

which

is

neither

too

hot

nor

too

cold

(between

—5°

and

40

°C/23°F

and

104

°F).

Leave

space

between

the

power

amplifier

and

the

wall

to

provide

good

ventilation.

Do

not

allow

a

curtain,

table

cloth,

etc.

to

block

the

ventilation

holes.

Keep

the

power

amplifier

away

from

direct

sunlight.

Do

not

place

close

to

a

heater.

Do

not

place

in

locations

subject

to

vibrations.

Do

not

place

in

locations

subject

to

dust.

Keep

as

far

from

a

tuner

and

a

preamplifier

as

possible

to

prevent

noise.

Power

cord

Do

not

handle

the

power

cord

with

wet

hands.

Do

not

bend

the

power

cord

double.

When

unplugging

from

the

wall

outlet,

always

pull

the

plug,

not

the

power

cord.

Malfunctions

Do

not

insert

any

metallic

object

inside

the

unit.

Do

not

allow

water

to

get

inside

the

unit.

Do

not

employ

thinner

or

benzine

to

clean

the

cabinet.

First

clean

with

a

neutral

cleaner

and

then

wipe

with

a

dry

cloth.

Power

switch

Do

not

plug

the

power

cord

into

an

AC

outlet

until

all

connections

are

complete.

Switch

the

power

off

when

connecting

other

components

to

it.

REAR

PANEL

1.

Connecting

with

other

components

may

result

in

trouble,

such

as

oscillation

or

hum.

Connect

ground

terminals

of

this

set

and

other

components

to

each

other.

SUBSONIC

and

DIRECT

INPUT

terminals

Do

not

connect

different

kinds

of

signals

simultaneously

to

input

terminals.

Input

cannon

connector

(for

professional

use)

(Unbalanced)

AC:

If

these

terminals

are

employed,

the

input

signal

passes

through

a

filter

having

a

cut-off

frequency

of

18

Hz

and

a

slope

of

6dB/oct,

which

results

in

a

reduction

of

ultra-low

frequency

noise,

such

as

that

encountered

with

warped

records,

and

prevents

speaker

intermodulation

distortion.

The

filter

also

eliminates

the

preamplifier

DC

leak

voltage,

thus

protecting

the

speakers.

DIRECT:

These

input

terminals

are

directly

connected

to

the

power

amplification

circuit.

Since

the

M-7050

employes

DC

amplifier

circuitry,

there

is

no

coupling

capacitor

between

the

input

circuit

and

the

power

amplification

stages.

Protective

circuit

When

the

protective

circuit

has

been

activated,

switch

off

the

power

and

determine

the

cause

as

follows:

The

speaker

load

impedance

Using

speakers

with

an

impedance

of

less

than

4

ohms

(or

a

short

circuit

across

the

speaker

terminals)

activates

the

protective

circuit

and

results

in

intermittent

sound

out-

put.

When

the

speaker

switch

is

at

the

“1

and

2”

position,

use

a

pair

of

speakers

having

an

impedance

of

8

or

high-

er,

at

“1”

or

“’2”

position,

use

a

speaker

of

4

or

higher.

Input

overload

The

speaker

produces

intermittent

sounds.

Detecting

the

offset

voltage

The

offset

voltage

of

+2

V

or

more,

activates

the

pro-

tective

circuit

and

results

in

no

sound

output.

Caution

indicator

When

the

protective

circuit

has

been

activated,

meter

illumination

changes

to

red.

TROUBLE

SHOOTING

What

seems

to

be

a

trouble

is

not

always

real

trouble.

{

Make

sure

first.

[

No

sound

]

Both

channel

Are

indicators

Yes

Does

the

relay

No

Is

the

speaker

switch

Yes

functioning?

operate?

set

to

ON?

One

channel

only

No

Reverse

the

L

and

R

Does

the

relay

Check

for

speaker

connections.

operate

connections

Does

the

channel

with

no

sound

shift?

No

Yes

Navsound

Yes

Is

the

input

level

volume

|

Yes

Check

for

trouble

in

the

preamplifier

IfOK......

set

to

maximum?

or

connected

component.

Both

No

channels

os

Does

the

replacement

of

the

preamplifier

or

connected

component

correct

distorted

sound?

|

Distorted

sound

only

Does

the

channel

with

distorted

sound

shift?

No

defect

in

the

M—7050

te

No

One

channel

Reverse

the

L

and

R

connections.

There

may

be

trouble

in

the

M—7050

it

self.

Consult

your

dealer.

BLOCK

DIAGRAM

YBLAW

8Y3MOd

ANddNS

YAMOd

39VLS

YSBAING

dWY

Y3M0d

A1ddNS

YAMOd

3OVLS

LNdLNO

TAA37

(00)

LOaYIa

@-WALSAS

Y3axVadS

(Ho

LINDYID

svia

v-y4adns

(Ov)

SINOSSNS

SANOHd

YOLINOW

Z2HOLIMS

LINDAID

SANILOSLOYd

Yy3ayvV3ads

LINDAID

Ssvig

(Sv)

SINOSSNS

(a4)

O

(10

(9q)

LOaYIa

T3A37

dWY

Y3aM0d

PERFORMANCE

GRAPHS

Wi

THD

vs.

Output

power

oe

|

;

=

&

0.03

=

|

ne

=a

{

c

Distortion

of

measurement

system

j

O

0.02

tae

4

1H

=

1KHz

0.0008%

7

6

20Hz

0,0011%

{

-_

20KHz

0.0014%

2

L.

pat

3

0.01

-

|

2

je

:

|

2

0.007

F

a

©

0.005

+

E

Ht

PS

0.003

g

0.002

°

ke

_——

|

KHz

0.001

-

+H

0.0007

=

1

rf

2

3

5

?

10

20

30

50

70

100

200

300

500

Power

output

(W/8

Q

}

@

Spectrum

of

harmonic

distortion

(dB)

—70

}

20K

100K

200K

}

20K

100K

200K

*

10

kHz

Fundamental

10

kHz

Fundamental

Measurement

System

Super—A

@

Characteristics

of

TIM

distortion

(Low

pass

filter

fe=100

kHz)

(dB}

3.18K

6.36K

9.54K

12.72K

15K

3.18K

6.36K

=

9.54K

=

12.72K

15K

19.08K

{He}

15.9K

(He)

15.9K

The

spectrum

of

input

signal

Output

signal

of

M-7050

(Same

as

input

signal)

af.

2

4

|

20K

100K

10

kHz

Fundamental

class

AB

3.18K

6.36K

9.54K

12,72K

15K

(Hz)

15.9K

An

example

of

TIM

distortion

(TIM

distortion

is

sum

of

components

less

than

15

kHz

which

showed

with

arrows.)

1g

O8K

TECHNICAL

DESCRIPTION

Super

A

power

amplifier

A

big

problem

has

remained

unsolved

in

the

progress

regarding

amplifier

technology:

how

can

class-A

operation

be

made

compatible

with

high

power

efficiency?

The

class-A

operation

is

best

in

terms

of

low

distortion;

its

critical

drawback

is

such

that

its

power

loss

is

greater

than

the

available

output

power.

Because

of

this,

class-B

amplifiers

have

generally

been

applied

for

power

amplification

because

they

offer

both

acceptable

distortion

and

power

efficiency.

However,

as

long

as

class-B

amplifiers

are

employed,

the

occurrence

of

crossover

distor-

tion

and

switching

distortion

is

inevitable.

Although

the

improvements

of

circuit

elements

have

realized

fairly

good

class-B

amplifiers,

when

their

values

of

distortion

are

referred

to,

the

‘‘nature”

of

distortion

is

still

detrimental

to

the

re-

produced

sound

quality.

To

solve

this

problem

by

improving

circuit

technology,

JVC

has

developed

its

new

‘’Super-A”’

power

amplifier.

The

Super-A

power

amplifier

consists

of

a

voltage

amplifier

stage

whose

distortion

is

minimized

by

compensating

for

the

non-linearity

of

semiconductors,

and

aclass-A

power

amplifier

stage

which

includes

a

bias

circuit

for

raising

the

power

effi-

ciency

to

such

a

degree

as

is

comparable

to

that

of

a

class-B

amplifier.

JVC’s

Super-A

power

amplifier

offers

the

following

features:

1)

Power

efficiency

is

extremely

high

despite

the

class-A

operation,

greatly

reducing

power

loss

and

heat

generation

compared

with

conventional

class-A

amplifiers.

2)

Switching

distortion

inherent

in

class-B

operation

is

com-

pletely

eliminated;

it

is

perfectly

zero.

3)

AVecE

distortion

*1,

ACob

distortion

*2

and

A

Vpe

dis-

tortion

“3

are

all

extremely

low

because

of

the

unique

non-distortion

circuit

configuration.

“1

Distortion

caused

by

non-linear

variations

of

current

gain

B

due

to

variations

of

collector-emitter

voltage

VCE.

*2

Distortion

caused

by

non-linear

variations

of

amplifier

gain

which

are

caused

by

non-linear

variations

of

feedback

capacity

Cob

due

to

variations

of

collector-emitter

voltage

VCE.

*3

Distortion

caused

by

non-linear

variations

of

base-emitter

voltage

VBE

of

power

transistor.

Distortion

of

measurement

system

Distortion

of

‘“Super—A”

Fig.

1

Output

and

residual

distortion

waveforms

of

measur-

ing

instrument

Fig.2

Output

and

distortion

waveforms

of

Super-A

am-

plifier

Fig.

3

Output

and

distortion

waveforms

of

class-AB

ampli-

fier

Voltage

amplifier

stage

utilizing

‘‘Super-A”’

performance

to

the

utmost

Fig.

4

shows

operating

characteristics

of

a

common-emitter

transistor;

8

varies

as

VCE

varies,

resulting

in

A

Vce

distortion

as

described

above.

Fig.

5

shows

a

variation

of

the

feedback

capacity

Cop

in

re-

lation

to

VCE.

This

non-linear

variation

of

Cop

due

to

varia-

tions

of

VCE

causes

a

non-linear

variation

of

the

amplifier

gain,

leading

to

the

A

Cob

distortion

mentioned

above.

Fig.

6

shows

operating

characteristics

of

a

common-base

transistor.

What

is

noteworthy

about

this

type

of

operation

is

that,

though

its

current

gain

is

O

dB,

its

output

linearity

in

constant-

current

drive

is

fairly

good

since

a

scarcely

varies

with

varia-

tions

of

VcE

(a=

1)

as

shown

by

the

equal

distance

between

adjacent

base

current

curves.

An

example

of

the

cascode-connected

amplifier

circuit

is

shown

in

Fig.

7.

The

features

of

this

circuit

are

good

frequ-

ency

response

(because

of

no

mirror

effect

due

to

Cob)

and

high

output

impedance.

This

means

that

this

circuit

eliminates

distortion

by

effectively

combining

the

advantages

of

common-emitter

and

base-emitter

configurations.

The

driver

stage

of

the

Super-A

power

amplifier

employs

an

applied

circuit

of

this

kind

and

a

drastic

reduction

in

distoriton

is

the

result.

Fig.4

Output

characteristics

of

common-emitter

amplifier

Fig.5

Cop

characteristic

Fig.6

Output

characteristics

of

common-base

amplifier

Fig.

7

Cascode

amplifier

Distortion

of

‘‘class

AB”

f=10

kHz,

THD=0.0008%

Fig.

1.

f=10

kHz,

Output

power=100W/8

QO,

THD=0.0009%

Fig.

2.

9

f=10

kHz,

Output

power=100W/8

Q

THD=0.0022%

Fig.

3.

IB1

Vee

Fig.

4.

Emitter

Configration

Vcs

Fig.

6.

Base

Configration

SPECIFICATIONS

Circuitry..........

Direct-coupled

DC

circuitry

with

F.E.T.

cascode

connected

double

differential

input

and

parallel-push

pull

output

SUPER-A

Output

power.......

150W

+

150W

892

Total

harmonic

distortion.........

0.0004%

(1KHz

150W

8&2)

(Mesured

by

Y.H.P.

HP-1B)

0.003%

(20Hz

~

20KHz,

150W

822)

0.03%

(20Hz

~

100KHz,

150W-822)

Inter

moduration

distortion.........

0.003%

(60

Hz:

7

kHz=

4:

1,8)

Power

bandwidth

....5

~

100KHz

(0.02%,

892,

IHF)

TIM

(Transient

Intermodulation

distortion)

........

unmeasurable

10

Fig.

5.

Cob

characteristic

Slew

Rate

........

Switching

distortion.

.

Hum

&

Noise......

Frequency

charactor

.

Subsonic

Filter.....

Input

sensitibity/

impedance.......

Output

..........

Power

suply.......

Power

consumption.

.

Dimensions

.......

Fig.

7.

Cascode

amplifier

+300V/p

sec.

.0

less

than

200

pV

(Short

circuit)

.DC

~

100KHz,

+0,

—0.2dB

18Hz

6dB/oct

.1V

(input

level

volume

max)

/47KQ

more

than

120dB

(1.H.F.A)

200(1KHz)

882

speaker-1

4Q.~

16Q

speaker-2

4Q.~

160

speaker

142

801~

162

Monitor

phone

Refer

to

page

30

.

Refer

to

page

30

160

m/m

(H),

425

m/m

(W),

415

m/m

(D)

22.4

kg

(49.3

Ibs)

Warning

:

When

replacing

the

parts

marked

with

A\

,

be

sure

to

designated

parts

to

ensure

safety.

Service

Manual

PRECAUTION

IN

SERVICING

PRECAUTIONS

FOR

SERVICING

AND

REPAIRING

1.

Removal

of

power

transformer

(replacement

of

transistor

and

parts

on

circuit

board)

Remove

the

power

transformer

before

replacing

the

transistor

mounted

on

a

heat

sink

and

parts

mounted

on

the

circuit

board

(TAP-279).

Follow

the

procedure

below.

1)

Remove

four

screws

(1)

and

then

cover

(2).

(See

Fig.

16.)

2)

Remove

three

screws

(3)

from

the

back.

3)

Remove

three

screws

(4)

from

the

top.

4)

Remove

four

screws

(5)

from

each

side.

5)

Disconnect

all

connectors

of

the

power

transformer

wiring.

(See

Fig.

8

for

how

to

disconnect

the

con-

nector

of

the

power

switch

wiring.)

6)

Remove

the

power

transformer

from

the

chassis

carefully

since

it

is

very

heavy.

(Do

not

let

it

bump

on

the

circuit

board

underneath.)

Disconnect

with

pushing

here.

Fig.

8.

Disassembly

of

front

panel

1)

Disconnect

all

connectors

of

the

front

panel

wiring

from

the

circuit

board.

(See

Fig.

8

.

for

how

to

dis-

connect

the

connector

of

the

power

switch-trans-

former

wiring.

2)

Remove

four

screws

(6).

Screws

(7)

need

not

be

removed.

3)

Remove

four

screws

(7)

to

disassemble

the

front

panel

assembly

into

the

meter

and

the

glass

panel.

4)

Holding

the

meter

vertically,

adjust

its

zero

point.

5)

Replace

the

wire

plugs

into

the

circuit

board

sockets,

paying

attention

to

their

direction.

Follow

the

indication

on

direction

marked

on

the

circuit

board.

(See

Fig.

9.)

Insert

the

sockets

to

direction

Ba

on

the

circuit

board.

Fig.

9.

(For

only

qualified

service

personnel)

Show

this

manual

to

service

personnel

when

servicing

SUPER-A

block

The

SUPER-A

bias

circuit

is

made

into

a

single

block

to

maintain

performance

including

temperature

characteris-

tics.

Trouble

occurring

in

the

SUPER-A

block

is

rarely

independent

of

other

stages.

Defects

of

a

stage

usually

affects

the

preceding

stage

adversely

and

finally

the

SUPER-A

block

suffers.

Starting

from

the

final

stage,

replace

defective

transistors.

When

‘the

stages

work

well,

check

the

SUPER-A

block

by

the

following

procedure.

(Refer

to

‘4.

Check

after

repair’’

for

the

sequence

of

turning

on

power.)

1)

Measure

the

voltage

developing

between

terminals

701

and

709

(X013’s

collector

and

test

point

F)

or

terminals

705

and

709

(X013’s

emitter

and

test

point

F)

using

a

multimeter

set

in

the

“1V

AC”

range.

Normally

it

reads

OV

when

no

signal

is

delivered

and

about

0.6V

for

the

1kHz

rated

output

(into

an

8-ohm

load).

The

SUPER-A

block

is

in

trouble

if

the

reading

is

greater

than

1V.

Check

the

R-channe!

in

the

same

way.

(In

the

R-channel,

check

voltage

between

X014

and

test

point

A.)

2)

Setting

the

multimeter

in

a

DC

range,

check

voltage

between

terminals

703

and

707

(X805's

emitter

and

X807's

emitter).

Normally

the

reading

varies

from

3.8V

to

4.3V

when

the

level

of

1kHz

input

signal

is

varied

from

zero

to

the

rated

output

(into

8-ohm

load).

The

SUPER-A

block

is

in

trouble

if

the

read-

ing

does

not

vary.

Replace

the

SUPER-A

block

as

a

unit

in

that

case.

Check

the

R-Channel

in

the

same

way.

(In

the

R-channel,

check

voltage

between

X806

and

X808.)

Check

after

repair

1)

Unplug

the

red,

white,

and

black

wires

of

TPS-

226.

(The

wires

connect

to

a

large

electrolytic

capacitor.)

Now

the

final

stage

is

not

supplied

with

power.

2)

Apply

1-kHz

signal

of

approximately

-—30dB

{30mV)

to

the

input

terminal.

Connect

an

oscillo-

scope

to

test

points

A

and

F

to

monitor

waveform.

3)

Start

supplying

power.

(If

a

varying-voltage

power

transformer

is

available,

you

can

raise

the

voltage

gradually

while

watching

the

waveform

on

the

oscilloscope

to

secure

safety.)

4)

If

you

see

the

waveform

shown

in

Fig.

19,

the

stages

up

to

the

driver

work

well.

(At

this

time

no

voltage

is

applied

to

the

final

stage

and

the

power

transistor

is

working

as

a

diode.)

Up

to

now

we

assume

that

the

final-stage

power

transistor

is

intact.

Confirm

in

advance

that

the

power

transistor

is

not

defective

after

disconnecting

it

from

the

circuit

board.

If

the

power

transistor

is

shorted

between

its

base

and

emitter,

the

drive

stage

will

be

shorted

and

damaged

(you

will

see

no

wave-

form).

Caution:

Never

connect

a

dummy

!oad

up

to

step

4:

the

drive

stage

will

be

overloaded

and

damaged.

Fig.

10.

5)

If

the

wrong

waveform

is

detected,

vary

the

input

voltage

from

OV

up

gradually

and

check

waveform

in

varying

voltage

ranges

of

the

oscilloscope.

if

the

right

waveform

is

not

obtained

yet,

check

transistors

and

resistors

in

the

circuits

using

a

multimeter.

The

resistors

marked

with

A\

in

the

circuit

diagram

are

liable

to

disconnection.

MEMO

RUNDOM

6)

When

the

waveform

of

Fig.

10

is

detected,

stop

supplying

power

and

plug

the

wires

into

the

sockets

of

TPS-226.

Then

start

supplying

power

while

you

monitor

waveform

at

the

test

points

with

the

input

voltage

kept

applied.

Do

not

connect

any

dummy

load

yet.

Normally

you

will

see

sine

waves

on

the

oscilloscope.

Carry

out

the

above

steps

for

both

channels.

At

this

time

the

output

voltage

exceeds

35V.

For

safety,

you

can

raise

the

voltage

gradually,

if

a

varying-voltage

power

transformer

is

available,while

you

watch

the

waveform.

Connect

a

dummy

load.

Normally

the

output

level

is

approximately

35V

over

an

8-ohm

load

(150W)

when

both

channels

are

driven

with

1-kHz

input

signal.

Even

if

the

SUPER-A

block

is

defective,

the

ampli-

fier

will

operate

in

class

B.

In

this

case,

check

the

SUPER-A

block

referring

to

‘3,

SUPER-A

block”’.

Referring

to

“Adjustment”

(page

13),

check

idling

current,

voltages

at

test

points,

voltage

gain,

and

frequency

response,

etc.

12

ADJUSTMENT

PROCEDURE

OF

AMPLIFIER

Adjustment

procedures

Left

channel——

|-—Right

channel

RY

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R732

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tras

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&

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METER

ADJ.

R42

RAI!

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TaP-279

/

Note:

Before

turning

on

the

power,

turn

R625

of

left

and

right

channels

to

middie

point

and

R411,

412,

R732,

R732

fully

counter-clockwise.

Fig.

11.

Idling

current

adjustment

of

the

power

amplifier

(TAD-279C)

As

illustrated

in

Fig.

11.

take

voltage

readings

between

the

testpointsof

A-B,

A-C,

A-D,

A-E,

F-G,

F-H,F-

J,

F-K

with

DC

millivoltmeters.

(Turn

on

the

power

switch

and

wait

for

5

minutes

and

then

start

the

adjustment)

First,

turn

R731

fully

counterclockwise

and

then

turn

it

clockwise

slowly

while

watching

the

DC

millivoltmeter

connected

bet-

ween

A-B

in

order

to

adjust

the

current

value

to

50

mV.

Similarly,

connect

the

DC

millivoltmeters

between

A-C,

A-

D,

A-E,

F-G

,

F-H,

F-J,

F-K

and

confirm

that

these

meter

read

40-60

mV.

(The

idling

current

becomes

80-120

mA).

If

the

millivoltmeters

do

not

read

80

—

120

mA,

turn

R731

slightly

for

adjustment.

Adjustment

of

the

power

output

meter

Before

turning

on

the

power,

set

R411,

412

to

middle

point.

Adjust

R411(left),

R412(right)

so

that

the

output

power

meter

shows

150

W

point

when

output

power

is

34.7

V

on

speaker

terminal.

13

Adjustment

of

the

offset

voltage

of

the

power

amplifier

(TAD-279C)

Before

turning

on

the

power,

turn

R625

of

left

and

right

channels

to

middle

point.

As

shown

in

Fig.

11.

connect

the

DC

millivoltmeter

between

the

testpoints

of

A

-ground,

and

then

turn

R625

slowly

so

that

the

meter

shows

as

low

a

value

as

possible,

(if

possible

“0”).

On

completion

of

the

adjustment,

wait

for

5—6

minutes,

and

confirm

whether

or

not

the

adjusted

voltage

varies

greatly.

Precautions

A

nonpolar

DC

millivoltmeter

is

preferable

for

the

above

adjustments.

If

polar

millivoltmeters

are

used,

pay

careful

attention

to

their

plus

(+)

and

minus

(—)

polarities.

Start

the

measurements

using

the

highest

meter

range.

CHECK

AFTER

SERVICING

31dB

(20

—

100kHz)

at

output

level

of

OdB

1.

Gain:

(0.77V).

2.

Hum

&

Noise

:

Below

0.2mV

(Short

circuit).

3.

Check

the

output

power

according

to

specification.

EXPLODED

VIEW

Parts

List

(Fig.

12.)

(Fig.

12)

Item

No.

Parts

Number

Rating,

Description

Parts

Name

O'ty

1

*E10342-002

Metal

cover

1

2

*E23224-001

Front

panel

ass’y

1

3

*E66097-001

Push

knob

assy

2

4

*E66096-001

Push

knob

ass’y

1

5

*E23106-002

Cover

1

6

*E23035-005

Right

Heat

sink

1

7

*E23035-006

Left

Heat

sink

1

8

*E03617-16

A\

Power

transformer

1

9

*E10343-001

Bottom

cover

1

10

*E23082-001

Right

Side

bracket

1

11

*E23082-002

Left

Side

bracket

1

12

E47227-007

Foot

4

13

SBSB4016M

Tapping

screw

4

14

£61660-001

Special

screw

4

EXPLODED

VIEW

Front

Panel

WJUUUUUULUUJUU

LULU

~

N

o

19

Parts

List

(Fig.

13)

_

TAP-279C

UPER-A

(TAD-198B)

-195(Right)

i}

=U

CI

TAD-195

(Left)

SUPER-A

LI

|_|

(__}

TAD

(TAD-198B)

oF}

www

17

16

15

16

22

42

18

«6

(Fig.

13)

i

!

JIL

TSC-124A

item

No.

Parts

Number

Rating,

Description

Parts

Name

15

EL80056

Black

Speaker

terminal

16

EL80055

Red

Speaker

terminal

17

E03619-001

Grand

terminal

18

E61212-001

Knob

19

Refer

to

page

30

A

Power

cord

20

Refer

to

page

30

A\

Cord

stopper

21

Refer

to

page

30

AV

Push

switch

(power)

22

-1

EL80051

18000

41/80

V

Electrolytic

capacitor

Q

2

N=]

424NnNNh

15

EXPLODED

VIEW

TSC-124A

TPS-227A

TAP-228A

(Fig.

14)

Parts

List

(Fig.

14)

Item

No.

Part

Number

|

Rating,

Description

Parts

Name

O'ty

23

i

QLP3101-322

Pilot

lamp

3

24

EL80052

Meter

assembly

2

25

E66102-002

Plate

2

26

E03468-007

Headphone

jack

1

27

E66136-001

Jack

holder

1

28

E66150-002

Stud

2

29

E23041-001

Mask

plate

1

30

£66228-001

Mark

1

31

E23042-001

Dial

back

panel

1

32

E23044-001

Meter

scale

1

33

E300124-002

Right

Holder

1

34

E300125-002

Left

Holder

1

35

E66476-001

Reflector

2

36

SBSB3008M

Tapping

screw

37

LPSP3008MS

Assembly

screw

TAP-228A

Lamp

circuit

board

2

TPS-227A

Relay

circuit

board

1

TSC-124A

Switch

circuit

board

1

16

EXPLODED

VIEW

(Fig.

15)

Parts

List

(Fig.

15)

Item

No.

Part

Number

Rating,

Description

Parts

Name

Q'ty

38

EL80059

{nput

jack

1

39

EL80049

Input

level

adjust

Variable

resistor

2

40

E66086-001

”

Volume

holder

1

41

Refer

to

page

30

A

AC

Outlet

1

42

E23036-002

Rear

panel

1

43

SASB3008N

Screw

EXPLODED

X007

(Left)

X008

(Right)

2941076

(G)

45

X005

(Left)

X006

(Right)

241076

(G)

X011

(Left)

X012

(Right)

2SB649A

(B,C)

X001

(Left)

X002

(Right)

28C2526

(G)

X013

(Left)

X014

(Right)

ae

ag

{

2SC

1568

(R)

je

\

X009

(Left)

\

X010

(Right)

2SD669A

(B,C)

\

/

\

X003

(Left)

i

\

X004

(Right)

28C2526(G)

!

|

nee:

Left

channel

X501

(Left)

2SD669A(B,C)

/

7

X502

(Right)

2SB649A(B,C)

\

6

Right

channe

(Fig.

16)

Sas,

toe

Parts

List

Fig.

16)

(

[

Item

No.

Parts

Number

|

Rating,

Description

|

Parts

Name

O'ty

44

E66150-001

Right

4

Pcs,

Left 4

Pcs.

Stud

8

45

E66088-001

L-Bracket

2

iF

|

an

Item

No.}

Part

Number

Rating

Description

Item

No.|

Part

Number

|

Rating

|

Description

Pc

fT

[

Pc

fT

Maker

x001

2SC2526

(G)

120

W

80

MHz

x009

2SD669A

(B,C);

1W

140

MHz

Hitachi

x002

2802526

(G)

120W

80

MHz

x010

2SD669A

(B,C);

1W

140

MHz

iM

X003

2SC2526

(G)

120

W

80

MHz

xo11

2SB649A

(B,C)}

1W

140

MHz

x004

2SC2526

(G)

120

W

80

MHz

x012

2SB649A

(B,C)|

1W

140

MHz

X005

2SA1076

(G)

120W

|

80MHz

X013

2SC1568

(R)

4w

150

MHz

Matsushita

X006

2SA1076

(G)

120w

|

80MHz

x014

2SC1568

(R)

4w

150

MHz

"

X007

2SA1076

(G)

120W

|

80MHz

X501

2SD669A

(B,C)|

1W

140

MHz

Hitachi

X008

2SA1076

(G)

120W

|

80MHz

2SB649A

(B.C)

|

1W

140

MHz

Hitachi

(

Note.

E

1.

Transistor

2C2526

(G)

(X001,

002,

003,

004)

can

be

replaced

with

2SC2565

(O)

(Toshiba),

2$(1076

(G)

(X005,

006,

007,

008)

can

be

replaced

with

2SA1095(O)

(Toshiba).

18

EXPLODED

VIEW

TAP-279C

Parts

List

(Fig.

17)

Item

No.

pea

Number

|

Rating,

Description}

Parts

Name

46

Refer

to

page30|

Power

Supply

C.

Board

47

E23043—003

Trans

bracket

:

48

Refer

to

page

30

Fuse

C.

Board

(Fig.

17)

49

E300400—005

Holder

50

E3001

15—002

H.sink

holder

51

Refer

topage

30

Plate

52

E66557—001

L-Bracket

53

Refer

topage

30

V.

Selector

54

SBSB3016M

Tap.

screw

55

SBSB4008M

Tap.

screw

22-2

EFZ-0079-684

|

100

V

0.68

UF

M.M.

Capacitor

CIRCUIT

BOARD

(BOTTOM

VIEW)

TAP-279C

(Base

circuit

board)

dino

(volavzzevsz

see,

OBR.

vg

©

LINDUID

(ae)

eT

=

ES

a

is

(Fig.

18)

20

JVC M-7050 User manual

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