Kenwood Th-77a User manual

144/440(430)MHz

FM

DUAL

BANDER

TH-77A/E

SERVICE

MANUAL

KENWOOD

PRINTED

IN

JAPAN

B51-8057-00(B)1105

————

CONTENTS

DISASSEMBLY

FOR

REPAIR.........:cscssceccscssssesesesseessseessvess

2

CIRCUIT

DESCRIPTION

...ccscccsscsccssesssseecesecsesesseessesenseensssee

4

DESCRIPTION

OF

COMPONENTS.

......cccescccscsesssseecsseeeene

16

SEMICONDUCTOR

DATA.

......cccsscssssescecseccescessesssecrecsersese

20

PARTS

LIST....ccsccsscsocscscssecsssescsssccsseessseeees

Be

ete

tee

29

Antenna

DISASSEMBLY

............0...ccccccecccssccessesssceescecsesenseseeccceneneees

48

(790-0414-05)

PAGKING

250.

ei.cs0cg:hs

accaceligseralisedsiuvitdessangdaoucaseverbicecseeteor

49

ADJUSTMENT

.......cssccssssssccssecccscsccsscsssececsecsusceracsnseesncessese

50

PC

BOARD

VIEWS/CIRCUIT

DIAGRAMS

-%

VHF

VCO

(X58-3740-00)

...ccssscsucccossccessececsrsnscneesnecsrseecses

55

bi

nen

Wvar)

UHF

VCO

(X58-3760-00)..-cssssscsovessssesossevssssscersessessecocesss

56

|

(K29-4570-04)x2

APC

1K502077

0-00)

(AVS

itect

aks

ots

ce

canes

57

|

be

PI,

(H5B597.70-0G)

1B)

cscavtasceetsdesescssaestanoeetasncivtencbtehes

58

SUB-U

(X59-37

70-00):

(Chsscacsercescctevadvivervesissnasnasosavsersie

59

Knob

(ENCODER)

NOISE

AMP

(X58-3770-00)

(D).ccccsecccesssseecsseccessseecneeereee

60

ie

Neo

aeee

4)

AM

(X59-3810-00)

(B)

..ssssscsssssssesscsvecessecaressnessescneecenesssse

61

Knob

(SQL)

.

f

B00

MHz

(X59-3810-00)

(A)

.sessssssssesecesecesessscsseersessssensees

62

(K29-4571-04)

ee

eet

CONTROL

UNIT

(X53-333X-XX)..ssssesceeeessssseeseessceseeneeees

63

Pee

TX-RX

UNIT

(X57-3630-XX)

(REV)

.vscesssseeersvesseestsesseeeses

67

|

TX-RX

UNIT

(X57-3630-XX)

(RFU)

.scsccessecsesccsecsecersseessves

69

SCHEMATIC

DIAGRAM

u....ccsscssscsecccsssscsecsseseuseseecacceeseesee

71

BLOCK

DIAGRAM......cscssscsssessssscscsseccsessesecstesrsesseenssesseesses

77

——"

ee

lee

cores

LEVEL

DIAGRAM.................cccccccccereeseccecceccssessccceececerseesees

79

-0975-03):

K,

P,

M,

TERMINAL

FUNCTIONS

..0....ccsscssssscscccesssecssssessesssssseenseess

81

ep

a

ie

BC-9

(BATTERY

CHARGER)

..ccccccccsssscssscccsssssssssceveeessooe

82

BT-6

(AAA

MANGANESE/ALKALINE

BATTERY

CASE)

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

82

BC-10

(COMPACT

CHARGER).........cccscsesessssescesssssessesssees

83

cis

i

BC-11

(RAPID

CHARGER)

.........cccccscsscsosecsescssesceccucsseereees

84

wu

DC-4/5

(MOBILE

CHARGER)............ccscsceccscssesseceueeseesseres

89

BC-12

(WALL

CHARGER)........cccscsssssccsesesesssssessesssessseenees

89

HMC-2

(HEAD

SET

WITH

VOX

&

PTT)

...scscsssessssessesssees

90

Battery

ass’y

HS-7/8/9

(EAR

PHONE)

............::cccsccsecceeeeesecssteeneenseeesenens

92

PB-5/6/7/8

(Ni-Cd

BATTERY)

.....sccsscsscesecsssccctsesssssseessses

93

PB-9/10

(Ni-Cd

BATTERY)

....c.ccssccoscssecesecseecssscasssccsseeseess

94

PG-2W

(DC

CORD)/PG-3F

(CORD

WITH

PLUG)............

95

SC-28/29

(SOFT

CASE)

...cccccessscsessssssscececsessscsesseecasessecesess

96

WR-1

(WATERPROOF

CASE)

.......cccscscececesssssccseecesecsesssees

96

SMC-31/32

(SPEAKER

MICROPHONE)

...........:++e-02e000++-

97

Photo

is

TH-77A.

SMC-33

(SPEAKER

MICROPHONE).........0...ccssecsssssseesoee

98

eter

to

parts

list

on

page

29.

TSU-7

(CTCSS

UNIT)

cesccssccsssssccssssssssessssccsssesscsssseeeeveee

99

SPECIFICATIONS.

.........ccsssessssssseeeetessseeeceees

BACK

COVER

IA-ffA/E

DISASSEMBLY

FOR

REPAIR

1.

Removing

the

case

1)

Remove

the

three

screws

from

the

side

faces

of

the

case

@).

2)

Remove

the

four

screws

holding

the

bottom

plate

(@)

.

3)

Remove

the

cap

from

the

panel

(@).

4)

Pull

up

the

front

case

off

the

panel

side

(@).

NOTE:

This

should

be

done

carefully

so

that

the

FPC

cabling

in-

side

the

case

is

not

accidentally

cut.

2.

Removing

the

control

unit

1)

Pull

out

the

connector

(@).

2)

Remove

the

five

knobs

and

three

nuts

(@)

.

3)

Detach

the

clamp

by

removing

the

two

screws

(@)

.

4)

Remove

the

two

screws

holding

the

printed

board

(Q).

5)

Raise

the

contro!

board

by

inserting

a

slotted

screwdriver

between

its

underside

and

the

front

case.

NOTE:

The

FPC

should

not

be

pulled.

TH-77A/E

DISASSEMBLY

FOR

REPAIR

3.

Disassembling

the

control

unit

1)

The

panel

is

fastened

by

the

claws

of

the

sub-panel.

Raise

3)

Remove

the

volume

encoder

from

the

panel

by

holding

its

the

sub-panel

by

bending

the

two

claws

(@).

rear

edge.

2)

Turn

down

the

board

by

bending

another

two

claws

(@).

General

exploded

view

of

control

unit

4)

Overall

disassembly

should

be

made

by

following

the

order

@-~6@

as

illustrated

on

the

right.

4.

Assembling

the

control

unit

1)

Hold

the

sub-panel

as

shown

on

the

right

and

fit

it

inside

the

panel!

by

aligning

the

heads

of

MIC/SP

jacks

to

the

holes

in

the

panel.

2)

Push

the

PTT

knob

and

control

board

into

position.

3)

Screw

down

the

control

unit,

but

after

tightening

the

round

nuts

of

the

volume

encoder

(for

positioning

purpose).

TH-77A/E

CIRCUIT

DESCRIPTION

(1)

Frequency

Configuration

The

TH-77

has

independent

PLL

circuits

and

intermediate-fre-

quency

amplifiers

for

the

VHF

and

UHF

bands.

A

VHF

signal

and

a

UHF

signal

can

thus

be

received

at

the

sz.1e

time.

The

UHF

signal

can

be

received

at

the

same

time

as

the

VHF

signal

by

doubling

the

local

oscillation

frequency

for

the

VHF

band.

(See

Figure

1.)

The

received

VHF

single

is

converted

to

the

first

intermediate

frequency

(IF)

of

45.05

MHz

using

the

first

local

oscillator,

fre-

quency

of

181.05

to

219.05

MHz,

and

is

mixed

with

the

second

local

oscillator

frequency

of

45.505

MHz

to

produce

the

second

IF

of

455

kHz.

The

received

UHF

signal

band

is

converted

to

the

first

IF

of

58.525

MHz

using

the

first

local

oscillator

frequency

of

371.475

to

391.475

MHz,

and

is

mixed

with

the

second

local

oscillator

136-174

MHz

(E2)

144~148

MHz

(K,

P,

M,

X)

144~146

MHz

(T,

E1)

430-440

MHz

(M,

T,

X,

E1,

£2)

438~450

MHz

(K,

P)

|44MHz

BAND

136~174

MHz

('st

MIX

45.05MHz

136-174

MHz

192.475

MHz

202.475

MHz

384.95

MHz~404.95

MHz

430MHz

BAND

371.4

MHz

$

391.4

MHz

VHF

PLL

frequency

of

58.070

MHz

to

produce

the

second

IF

of

455

kHz.

The

local

oscillator

frequency

for

the

VHF

band

is

doubled,

when

the

UHF

signal

is

received

at

the

same

time.

The

UHF

signal

is

converted

to

the

first

IF

of

45.05

MHz

for

the

VHF

band

using

a

frequency

of

384.95

to

404.95

MHz

obtained

when

the

first

loca!

oscillator

frequency

of

192.475

to

202.475

MHz

for

the

VHF

band

is

doubled.

The

resulting

frequency

is

mixed

with

the

second

local

oscillation

frequency

of

45.505

MHz

to

pro-

duce

the

second

IF

of

455

kHz.

As

described

above,

signal

reception

for

the

VHF,

UHF,

or

sub-

UHF

band

is

based

on

a

double-conversion

system.

In

the

transmit

signal

channel,

a

directly

oscillated

voltage-controlled

oscillator

(VCO)

signal

for

the

VHF

and

UHF

bands

is

sent

to

the

reactance

modulator,

amplified

to

the

required

level

by

a

linear

amplifier,

and

transmitted.

455

KHz

455

KHz

12.8

MHz

REF

OSC

ae

MIC

AMP

(2.8MHz

Fig.

1

Circuit

configuration

by

frequency

In-//A/C

CIRCUIT

DESCRIPTION

(2)

Receive

Signal

Channel

The

TH-77

uses

common

antenna

for

the

VHF

and

UHF

bands,

so

it

has

an

internal

duplexer.

The

TH-77

also

incorporates

two

audio

amplifiers

for

internal

and

external

speakers.

(See

Figure

2.)

[

Item

Rating

Nominal

center

frequency

(fo)

45.050

MHz

Pass

bandwidth

fo

+7.5

kHz

or

more

at

3

dB

Attenuation

bandwidth

fo

+22

kHz

or

less

at

25

dB

Guaranteed

attenuation

80

dB

or

more

within

fo

+910

kHz

Spurious:

40

dB

or

more

Ripple

1.0

dB

or

less

Insertion

loss

4.0

dB

or

less

Terminal

impedance

8002/2

pF

Table

1

MCF

(L71-0409-05)

(TX-RX

unit

XF1)

—s

Item

Rating

Nominal

center

frequency

(fo)

Pass

bandwidth

58.525

MHz

fo

+8.5

kHz

or

more

at

3

dB

Attenuation

bandwidth

fo

+25

kHz

or

less

at

25

dB

fo

+70

kHz

or

less

at

60

dB

Guaranteed

attenuation

80

dB

or

more

at

fo

+910

kHz

Ripple

Insertion

loss

Terminal

impedance

Center

frequency

of

6

dB

bandwidth

(fo}

6

dB

bandwidth

40

dB

bandwidth

1.0

dB

or

less

4.0

dB

or

less

3802/3.5

pF

Table

2

MCF

(L71-0410-05)

(TX-RX

unit

XF201)

455

kHz+1.5

kHz

+7.5

kHz

or

more

+15

kHz

or

less

Ripple

Guaranteed

attenuation

1.5

dB

or

less

(455

kHz+1.5

kHz)

27

dB

or

more

within

fo

+100

kHz

Insertion

loss

6

dB

or

less

Terminal

impedance

Table

3

Ceramic

filter

(L72-0362-05)

(IF

unit

CF1,

CF2)

1.5

kQ

2-1

VHF

Receiving

Block

The

signal

from

the

antenna

is

passed

through

a

low-pass

fil-

ter,

a

duplexer,

and

antenna

switches

D4

(M1808)

and

D5

{MA77),

and

amplified

by

Q7

(2SK360).

The

unwanted

band

components

of

the

signal

are

eliminated

by

a

bandpass

filter.

The

resulting

signal

is

mixed

with

the

first

local

oscillator

fre-

quency

by

first

mixer

Q6

(2SC4083),

and

converted

to

the

first

IF.

The

unwanted

components

of

the

converted

first

IF

signal

are

attenuated

by

a

pair

of

MCFs

and

amplified

by

IF

amplifier

Q5

(2SC4619).

The

signal

is

then

input

to

1C2

(MC3372D).

The

input

signal

of

IC2

is

mixed

with

the

second

local

oscillator

fre-

quency,

and

converted

to

the

second

IF.

The

unwanted

com-

ponents

of

the

converted

signal

are

attenuated

by

a

ceramic

fil-

ter.

The

resulting

signal

is

amplified,

then

detected

by

a

quad-

rature

detector

to

produce

an

AF

signal.

2-2

UHF

Receiving

Block

The

signal

from

the

antenna

is

passed

through

a

low-pass

fil-

ter,

a

duplexer,

and

antenna

switches

D204,

D205

(M1808),

and

D206

(MA77),

then

amplified

by

Q207

(2SC4226).

The

sig-

nal

is

then

split

into

the

main

UHF

and

sub-UHF

bands

by

a

power

divider.

The

unwanted

band

components

of

the

signal

are

attenuated

by

a helical

filter.

The

resulting

signal

is

amplifi-

ed

by

0206.

The

signal

is

mixed

with

the

first

local

oscillator

fre-

quency

by

first

mixer

Q205

and

converted

to

the

first

IF,

and

the

unwanted

components

are

attenuated

by

a

pair

of

MCFs.

The

signal

is

then

amplified

by

IF

amplifier

Q210

(2SC4215),

and

in-

put

to

IC202

(MC3372D).

The

resulting

signal

is

detected

by

a

quadrature

detector

to

produce

an

AF

signal

in

the

same

way

as

in

the

VHF

receiving

block.

2-3

Sub-UHF

Receiving

Block

The

signal

from

the

antenna

is

input

to

the

UHF

receiving

block.

The

input

signal

of

the

UHF

receiving

block

is

amplified

by

Q207,

split

by

a

power

divider,

and

input

to

the

sub-UHF

receiv-

ing

block.

The

signal

amplified

by

Q201

(2SC4226)

is

passed

through

a

bandpass

filter

to

attenuate

unwanted

signal

compo-

nents.

The

signal

is

then

mixed

with

a

frequency

twice

the

first

local

oscillator

frequency

for

the

VHF

band

by

first

mixer

Q202

(2SC

4083),

then

converted

to

the

first

IF

for

the

VHF

band.

The

VHF

receiving

block

is

used

for

the

signal

flow

following

the

first

IF

signal.

The

collectors

of

the

first

mixers

for

the

sub-UHF

and

VHF

bands

are

placed

facing

each

other

to

prevent

the

first

mixers

being

influenced

by

other

bands

when

the

bias

is

turned

on

or

off.

IFI-/

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CIRCUIT

DESCRIPTION

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Fig.

2

RX

section

block

diagram

IA-f

fA/E

CIRCUIT

DESCRIPTION

2-4

Audio

Circuit

®

Outline

The

AFV

and

AFU

signals

that

are

deemphasized

in

the

trans-

mitting-receiving

unit

are

input

to

control

unit

IC3

(TC4066BF)

and

separated

into

the

main

signal

and

subsignal.

The

separat-

ed

signals

are

passed

through

high-pass

filters

and

input

to

IC4,

which

performs

speaker

selection

and

mix/separate

se-

lection.

The

resulting

signals

are

amplified

by

IC5

and

IC6

(NJM386BM)},

then

output.

2-4-1

CTCSS

and

DTSS

selection

Input

of

the

AFV

and

AFU

signals

to

the

CTCSS

unit

and

DTMF

decoder

is

switched

by

the

CBC

and

DTB

signals.

The

CBC

and

DTB

signals

are

unstable

when

the

CTCSS,

DTSS,

and

paging

functions

are

off.

Figure

3

shows

the

port

status.

2-4-2

Received

audio

signal

selection

The

audio

signals

for

the

VHF

and

UHF

bands

are

separated

in-

to

the

main

signal

and

subsignal

by

IC3.

IC3

opens

all

switches

for

muting

when

it

outputs

a

BEEP

pulse.

IC4

performs

speaker

selection

and

mix/separate

selection.

Figure

4

shows

the

port

status.

AFV

(VHF

AF)O

AFU

(UHF

AF}

O

ane

a

Fig.

4

RX

audio

switching

circuit

Sub

VOL

Main

VOL

CBC

DTB

(CTCSS

SW)

(DTSS

SW)

CTCSS

Unit

AFV

Decode

input

(VHF

AFIO

To

DTMF

Decode

IC

AFU

(UHF

AFIO

DTB

Fig.

3

CTCSS,

DTSS

switching

circuit

AF

CONTROL

Ic

4

©

EXT.

SP

*

When

the

normal

separate

mode

is

set,

the

subband

is

heard

on

the

internal

speaker

and

the

main

band,

on

the

external

speaker.

In-//A/CO

CIRCUIT

DESCRIPTION

2-4-3

External

speaker

detection

The

microcomputer

detects

that

the

REM

of

the

speaker

jack

is

zero

or

the

remote

switch

voltage

when

the

speaker

plug

is

inserted.

The

audio

input

is

then

switched

from

IC6

to

IC5

by

IC3.

2-4-4

Audio

amplifier

Amplifier

IC6

(NJM386BM)

is

used

for

the

internal

speaker,

and

amplifier

C5,

for

the

external

speaker.

The

power

for

IC6

and

IC5

is

produced

by

016

(2SB1182)

and

Q17

(2SC4617).

D4

(MA110)

and

O18

(DTA144WE)

are

a

power

on/off

control

cir-

cuit.

2-4-5

Squelch

circuit

Since

the

squelch

circuit

for

the

UHF

band

is

configured

identi-

cally

to

that

for

the

VHF

band,

only

the

squelch

circuit

operation

for

the

VHF

band

is

described

below.

The

detection

output

sig-

nal

of

C2

is

filtered

by

an

internal

amplifier

in

IC2.

The

noise

components

of

the

signal

are

amplified

by

013.

The

resulting

signal

is

rectified

by

D16

to

produce

a

squelch

signal.

The

volt-

age

at

the

input

of

Q11

is

turned

on

or

off

by

the

squeich

var-

iable

resistor.

The

SCV

signal

and

hysteresis

switches

are

acti-

vated

by

Q12.

2-4-6

Signal-strength

meter

circuit

The

TH-77

employs

signal-strength

meter

circuits

|C2

and

1C202

(MC3377D)

for

the

transmitting-receiving

unit.

For

the

VHF

band,

the

microcomputer

input

voltage

is

adjusted

by

VR1

of

the

transmitting-receiving

unit.

For

the

UHF

band,

it

is

ad-

justed

by

VR6

of

the

control

unit.

The

liquid-crystal

display

for

the

VHF

and

UHF

bands

appears

at

the

same

time.

Each

signal-

strength

meter

signal

is

thus

added

to

the

input

pins

of

differ-

ent

analog-to-digital

converters.

The

liquid-crystal

display

con-

sists

of

five

steps

in

a

pair

for

the

VHF

and

UHF

bands.

TH-77A/E

CIRCUIT

DESCRIPTION

(3)

Transmit

Signal

Channel

3-2

Drive

Circuit

and

Final-Stage

Amplifier

In

the

transmit

signal

channel,

a

directly

oscillated

voltage-con-

The

voltage-controlled

OUTBUTS

for

the

VHF

and

CHE

pends

ale

trolled

oscillator

(VCO)

signal

for

the

VHF

and

UHF

bands

is

sent

to

two-stage

amplifiers,

then

amplified

to

the

reaniied

sent

to

the

reactance

modulator.

The

output

levels

of

the

mi-

level

by

the

RF

power

amplifier

module.

The

amplified

output

crophone

amplifiers

for

the

VHF

and

UHF

bands

can

be

adjust-

signals

are

passed

through

the

antenna

switches

for

the

VHF

ed

independently.

(See

Figure

5.)

and

UHF

bands,

and

sent

through

a

duplexer

and

lowpass

filter

3-1

Modulator

Circuit

to

the

antenna.

The

audio

signal

from

the

microphone

is

sent

to

control

unit

!C1

(NJM4560M),

then

a

preemphasis

circuit,

amplifier,

limiter

am-

plifier,

and

splatter

filter.

The

signal

is

then

selected

for

the

VHF

and

UHF

bands

by

Q12.

The

frequency

deviation

can

be

adjust-

ed

by

VR3

and

VR4.

The

modulation

signal

is

applied

to

a

vari-

cap

diode

for

voltage-controlled

oscillator

modulation

for

the

VHF

and

UHF

bands,

then

sent

to

the

reactance

modulator.

The

input

pins

are

jumpered

by

Q11

when

a

dual-tone

multifre-

quency

(DTMF)

is

used.

144

MHz

band

430

MHz

band

Low

frequency

VCO

(VHF)

Buffer Buffer

Excitation

esis

25238

(KI)

rae

oe

sao

(ee

SAva24

NJM4560M

284083

28C4083

2SCA215

2SC3356

S-AV22A

Buffer

amplifier

2S8C4215

PLL

eu

amplifier

M56760FP

2SC4116

CPU

#PD751

|6GF

HD404608

PLL

M56760FP

Buffer

amplifier

28C4226

REF

OSC

2804116

UH

Buffer Buffer

Excitation

Power

VCO(UHF)

amplifier

amnpihe

2SKSOBNV

(K52)

2804226

284226 284226

2sc4093

§-AU26

Fig.

5

Transmitter

system

block

diagram

T

10

H-77A/E

CIRCUIT

DESCRIPTION

3-3

APC

Circuit

The

automatic

phase

control

(APC)

circuit

produces

attain

a

stable

transmission

output.

This

circuit

also

detects

the

current

of

the

final-stage

amplifier

and

controls

the

input

power

level

of

the

amplifier.

ee

L

Table

4

The

APC

circuit

operation

for

the

UHF

band

is

explained

below

(Figure

6).

During

transmission,

04

is

turned

on

by

the

5TV

and

5TU

signals,

and

IC1

is

activated.

The

output

power

of

IC101

is

detected

as

the

voltage

drop

across

R4

and

R5.

The

voltage

at

both

ends

of

D1,

whichis

completely

stabilized

by

the

constant

current

source

of

01,

is

compared

with

the

voltage

divided

by

VR1,

R11,

and

VR2.

The

current

flowing

through

D101

is

con-

trolled

so

that

no

voltage

difference

occurs.

Consequently,

the

drive

input

power

of

|C101

decreases

when

the

power

amplifi-

er

module

current

increases,

and

the

drive

power

increases

when

the

module

current

decreases.

For

high-,

middle-,

and

low-level

selection,

Q2

and

Q3

are

turned

on

then

off

when

the

H/L1

and

H/L2

ports

are

con-

trolled.

The

reference

voltage

for

!C1

is

then

switched.

(See

Table

4.)

O

HA2

H/LI

STV

Fig.

6

APC

circuit

O

STU

Ic

101

Q2,93

Q7,Q98

Ql

Q4

1cl

R4,R5

UHF

Power

Amplifier

BAND

SW

UHF

POWER

SW

VHF

POWER

SW

CONSTANT

CURRENT

SOURCE

APC

AMP

SW

OC

ERROR

AMP

CURRENT

DETECT

Kenwood TH-77A User manual

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