Marantz 112 - Block Diagram of the AN217

1. INTRODUCTION
This
service
manual
was
prepared
for
use
by
Authorized
Warranty
Stations
and
contains
service
information
for
Marantz
Model
112
Stereophonic
Tuner.
Servicing
information
and
voltage
data
included
in
this
manual
are
intended
for
use
by
the
‘knowledgeable
and
experienced
technician
only.
All
instructions
should
be
read
carefully.
No
attempt
should
be
made
to
proceed
without
a
good
understanding
of
the
operation
of
the
tuner.
The
parts
list
furnishes
information
by
which
replacement
parts
may
be
ordered
from
the
Marantz
Company.
A
belief
description
is
included
for
parts
which
can
be
usually
be
obtained
through
local
suppliers.
|
2. AM TUNER
The
AM
Tuner
section
of
the
Model
112
is
contained
in
the
AM/IF
circuit
package
consisting
of
one
IC
H202
(AN217)
and
three
transistors.
The
IC
is
shown
in
Figure
1
in
the
block
diagram
form.
The
respective
three
transistors
serve
as
RF
amplifier,
|F
amplifier
for
intensifying
the
gain
of
the
IC,
and
audio
amplifier
for
magnifying
the
detected
audio
signal.
-AMPLIFIER(1)
AMPLIFIER(2)
LO AMPLIFIER ~T
Figure 1. Block Diagram of the AN217
AM MIXER
(1 3) &
s
OSCILLATOR
»
The
IC
includes
an
FM
IF
section
and
AM
Tuner
section,
each
of
which
comprises
two
functional
blocks.
The
first
block
of
the
FM
IF
section
is
an
FM
IF
amplifier
(1),
the
input
of
which
is
fed
from
pin
@,
and
the
output
is
led
to
pin
@).
The
second
block
is
an
FM
IF
amplifier
(2),
the
input
of
which
is
fed
from
pin
@
and
the
output
is
led
to
pin
.
The
first
block
of
the
AM
Tuner,
on
the
other
hand,
is
an
AM
mixer
and
oscillator,
the
input
of
which
is
fed
from
pin
43
and
the
output
is
led
to
pin
(2
.
The
second
block
is
an
AM
IF
amplifier,
the
input
of
which
is
fed
from
pin
@)
and
the
output
is
led
to
the
pin
()
.
All components except the tuning capacitor and ferrite bar antenna are mounted on the
printed circuit board P200.
An
AM
signal
induced
in
the
ferrite
bar
antenna
is
led
to
the
base
of
the
RF
amplifier
transistor
(H209)
and
amplified
to
a
level
required
for
overcoming
the
conversion
noises,
thus
giving
good
S/N
performanée.
The
tuned
circuit
inserted
in
each
of
the
output
and
input
circuits
of
the
RF
amplifier
assures
very
high
image
and
spurious
rejection
performance.
Then,
the
amplified
and
selected
AM
signal
is
fed
to
one
input
(pin
(3.
)
of
the
Mixer
section
of
the
IC(H202)
(pin
43
).
While
the
local
oscillator
voltage
is
injected
to
the
other
input
(pin
)
of
the
section
through
the
capacitor
C244.
Then,
both
AM
signal
and
local
oscillator
signal
are
mixed
and
converted
into
455kHz
intermediate-frequency
signal.
The
resulting
IF
signal
is
led
to
the first
IF
transformer
L205
consisting
of
one
ceramic
filter
and
two
tuned circuits.