Marantz 105B User Manual download pdf (Page 3)

I

NTRODUCTI

ON

This

ser

vi

ce

m

an

ual w

as

prepared f

or

u

se

by

A ut h

or

iz

ed

Warranty Stations and contains service

i

nf

ormation

for

Marantz

Mod

el

l 05B Stereophonic T

un

er.

Servicing in

for

mat

io

n

an

d v

ol

ta

ge

data included in this manual

are

intended

for

use

by

the

k

no

w ledgeable and experienced technician only.

All

instruction

should

be

read

carefully. No

at

t empt shou ld be m

ade

to proc

eed

wit

h

out

a good understanding

of

the operation in the

t uner.

The

part

lists furnish

infor

mation by which replacement part may

be

ordered

from

the

Marantz Com

pa

ny. A sim ple descrip

tio

n

is

included for parts which can

be

usually

be

obtained

th

rough local suppliers.

Th

e

Mod

el 1058

is

a

tu

ner version

of

the Marantz

's

Model

20

15

Tu

ner/Amplifier

and

almostthe

sam

e circu

itr

y as u

se

d in t he Model

201

5 is empl

oy

ed except

the

audio

Amplifier,

and power

su

pp

ly

circu

it

.

1.

AM

Tuner

A ll components exce

pt

ferrite bar

an

te

n

na

are

mounted on a printed

circuit

board

Pl00.

T

he

AM

signals induced in a

ferrite

bar antenna

are

applied

to

the

base

of

converter transistor

H113

t hrough a capacitor

of

C171,

whil

e t

he

loca l o

sci

llat

or

voltage

is

injected

to

the

emitter

of

H113

t hrough a capacitor C172. Bo

th

AM signa

ls

and oscillating voltage

are

mixed

at

the

base-

em

itter

ju

nctio

n and converted

int

o 455KHz intermediate frequency. The resulting I F signal

is

ap

plied

to th

e f

ir

st I F

tr

ansformer L 116 consisting

of

one ceramic

filter

and

two

tuned circuits.

T he o

utp

ut

of L11 6

is

le

d

to

the tra

ns

istor H 1

04

which in

turn

apply its

output

to

the

t

ra

nsist

or

of

next stage

Hl05.

T

he

fu

lly amplif ied IF

output

is

then applied

to

the diode H123

to

detect audible

si

g

na

l

th

rough the

det

ector tra

ns

f

ormer

L 117. The detected audio signal

is

filtered

and

th

e final

au

dio

out

put

is

obtained

from

pin terminal J118 and applied:

to

the

output

jacks

th

rou

gh

the

funct

io

n sw

it

ch.

The DC c

om

ponent

of

the detected I F

sig

n

al

is

used

as

a AGC voltage

to

control

emitter

c

urr

ent

of

H 104

th

rough

th

e resistor R 185. A part

of

I F signal

output

is

also applied

to

the diode

H

124

th

rough a capac

itor

C1BO

and rectif ied to obtain

DC

current

for

energizing the

AM

signal

stre

ng

t h meter

M0

01.

1.1 Suggestions

for

AM

Tuner

trouble

shooting

Che

ck

f or broken A M bar antenn

a,

next

try

to

tune station

by

rotating fly-wheel

tuning

knob

sl

o

wly

and observe the

AM

sig

n

al

streng

th

meter whether

it

deflects

or

not.

If

the signal strength

me

ter

gi

ves a

deflection

at

se

ver

al

fr

equencies received, no failure may exist in the

stages

at least

preceding f inal I F transf

or

m

er

L 117. N

ext

connect a oscilloscope

to

the pin terminal J118 and

ch

ec

k

for

aud io signa ls w it h the

tuning

meter deflected.

If

the signal strength meter does

not

deflect, check the local

osc

illa

tor

circu it. Norm

al

oscillating voltage at the

hot

end

of

the

osci

llator

tuning

ca

p

acitor

is

about 2

or

3 volts, varying

with

tuning

capacitor position. When

me

asu

ring oscillating voltage

use

a RF V

TV

M, no

circuit

tester gives correct indication.

If

the

local osci llator

volt

age

is

normal, check all voltage dist

rib

u

tion

in

the

AM

circuits by using a

DC

VTVM

and com pare t he measur

ed

values

with

those given in the schematic diagram.

2.

FM

Tuner

A ll components

are

m

ou

nted on a printed circ

uit

board P100.

FM signa ls induced by a FM

an

tenna are l

ed

to

FM antenna coil L 101.

These signals are then applied to t he FET RF

amplifier

which in

turn

applies its

output

to

the

next

transis

to

r mixer

Hl02

th

rough a hi

gh

Q

tuned

circuit.

The

mixer

convert its in

put

sign

al

int

o

10.71V1

Hz

intermediate frequency and amplifies

it

at the

same

ti

m

e.

The

H1

03

is

a local o

sc

illator

and its

output

is

injected

into

the

base

of

mixer

t r

an

s

is

to

r, t

he

inject ion voltage

is

a

bo

ut

40mV.

1

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