Sanyo PLUS T35 - FM Tuning Display and Recording Level; FM Tuning Display Operation; REC. LEVEL Switch Function

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FM

tuning

display

The

FM

tuning

display

is

given

in

the

upper

part

of

the

dial

scale

with

three

LEDs

in

the

form

of

(

>:

).

The

principle

of

FM

tuning

display

is

to

pick

up

IF

S-curve

of

FM,

compare

the

central

voltage

in

operational

amplifier

to

detect

the

center

output,

and

light

up

the

LED

for

center.

Also,

the

positive

potential

and

negative

potential

are

detected

in

the

operational

amplifier

to

check

whether

the

tuning

is

deviated

to

the

right

or

left

with

respect

to

the

dial

scale,

so

that

the

corresponding

LED

is

illuminated.

The

S-curve

signal

is

taken

out

from

pin

No.

7

and

pin

No.

10

of

Q203,

and

is

fed

into

Q408

(operational

amplifier).

Q408

comprises

two

operational

amplifiers.

In

operational

amplifier

(B),

the

comparative

voltage

is

taken

small

to

detect

the

center,

and

the

voltage

is

shaped

and

inverted

in

0419

(inverter),

and

the

LED

[-]

for

center

(LED

6,

green)

is

driven

by

0417

to

light

it

up.

In

opera-

tional

amplifier

(A},

on

the

other

hand,

the

positive

potential

and

negative

potential

of

the

input

signal

voltage

are

detected:

if

the

potential

is

positive,

Q415

is

turned

on,

and

the

voltage

is

shaped

and

inverted

by

0419,

so

that

the

right

side

deviation

mark

LED

[

»

]

(LED

5,

red)

is

illumi-

nated,

and

if

the

potential

is

negative,

0414

is

turned

on,

and

the

voltage

is

shaped

and

inverted

by

0419

twice,

so

that

the

left

side

deviation

mark

LED

[

<

]

(LED

4,

red)

is

iluminated.

Meanwhile,

0417

is

controlled

by

Q416,

which

is

intended

to

prevent

the

center

LED

from

lighting

up

when

the

signal

intensity

is

below

LEVEL

1.

Q203

LAI231

Q204

LBIG16

5

BIT

LEVEL

METER

—14—

Q408

RC

4558

OP-AMP

X

2

REC.

LEVEL

Switch

,

As

this

switch

is

turned

ON,

voice

of

FM

broadcasting

is

cut

off,

and

reference

signal

in

time

of

recording

is

fed

to

the

amplifier

or

tape

deck

from

the

output

terminals.

Reference

signal

is

a

sine

wave

of

about

400

Hz

having

the

level

corresponding

to

50%

modulation

(the

maximum

value

of

voice

signal)

or

FM

wave

produced

by

the

oscillator

(0310

jointly

used

with

AF-AMP.)

built

into

this

set.

Consequently,

if

recording

level

is

set

to

agree

with

this

reference

signal,

good

recording

become

posseble

easily.

Oscillation

circuit

is

used

jointly

with

the

Q310

(MJM-

4558)

of

the

AF-AMP.

FM

-

POWER

SUPPLY

Q419

TC4049

INVERTER

X

6

LED

4

(RED)

LEFT