Marantz 2245 - Introduction; AM Tuner Operation

INTRODUCTION
This
service
manual
was
prepared
for
use
by
Authorized
Warranty
Stations
and
contains
service
information
for
Marantz
Model
2245
Stereophonic
Receiver.
Servicing
information
and
voltage
data
included
in
this
manual
are
intended
for
use
by
the
knowledgeable
and
experienced
technician
only.
All
instruction
should
be
read
carefully.
No
attempt
should
be
made
to
proceed
without
a
good
understanding
of
the
operation
in
the
receiver.
The
parts
list
furnish
information
by
which
replacement
part
may
be
ordered
from
the
Marantz
Company.
A
simple
description
is
included
for
parts
which
can
be
usually
be
obtained
through
local
suppliers.
1. Service Notes
As
can
be
seen
from
the
circuit
diagram
the
chassis
of
Model
2245
consists
of
the
following
units.
Each
unit
mounted
on
a
printed
circuit
board
is
described
within
the
square
enclosed
by
a
bold
dotted
line
on
the
circuit
diagram.
1.
FM
FrontEnd
1...
00.
ee
ee
_
mounted
on
P.C.
Board,
P100
2.
FMIF
Amplifier
2...
0
ee
_...
mounted
on
P.C.
Board,
P200
3:
(PM
Detector
Gover
eee
Boe
ke
HA
ee
Dw
ks
mounted
on
P.C.
Board,
P500
4,
MPX
Stereo
Decoding
Amplifier
2...
00.
ee
ee
eee
mounted
on
P.C.
Board,
P300
5.
Muting
Control
Amplifier...
--
6-6-0
ee
eee
ees
mounted
on
P.C.
Board,
P550
6
SAM
TunerUAit
o
4c8
Sida
we
ce
ae
Ge
We
eS
mounted
on
P.C.
Board,
P150
7.
Phone
Amphtier
..ccwe
Ge
eee
So
eo
Rees
ssestan
as
ec
mounted
on
P.C.
Board,
P700°
8.
Tone
Amplifier
cts
tues
oad
ae
i
ahs
Bn ee
Oe
ee
mounted
on
P.C.
Board,
P400.
9.
Power
Amplifier
.
50.
eb
de
eee
mounted
on
P.C.
Board,
P750_
10.
Regulated
Power
Supply
and
Protection
Relay
Circuit...
.
mounted
on
P.C.
Board,
P800
11,
Loudness,
High
and
Low
Filter,
and
Muting
Switch
Unit
. . .
mounted
on
P.C.
Board,
P600
2;
AM
Tuner
All
components
except
Tuning
capacitor
and
ferrite
bar
antenna
are
mounted
on
a
printed
circuit
board
P.150.
The
AM
signals
induced
in
a
ferrite
bar
antenna
are
applied
to
the
base
of
RF
amplifier
transistor
H151
through
a
capacitor
of
C151
and
amplified
to
the
level
required
for
overcoming
the
conversion
noises,
thus
giving
good
S/N
performance.
The
tuned
circuits
inserted
in
both
out
and
input
circuit
of
the
RF
amplifier
assure
very
high
image
and
spurious
rejection
performance.
Thus
amplified
and
selected
AM
signals
are
then
applied
to
the
base
of
converter
transistor
H1i52
through
a
coupling
capacitor
C156.
While
the
local
oscillator
voltage
is
injected
to
the
emitter
of
H152
through
a
capacitor
C157.
Both
AM
signals
and
oscillating
voltage
are
mixed
at
the
base-emitter
junction
and
converted
into
455KHz
intermediate
frequency.
The
resulting
IF
signal
is
applied
to
the
first
IF
transformer
1153
consisting
of
one
ceramic
filter
and
two
tuned
circuits.
The
output
of.
L153
is
led
to
the
transistor
H153
which
in
turn
apply
its
output
to
the
transistor
of
next
stage
H154.
The
fully
amplified
IF
output
is
then
applied
to
the
diode
H157
to
detect
audible
signal
through
the
detector
transformer
L154.
The
detected
audio
signal
is
filtered
and
amplified
and
the
final
audio
output
is
obtained
from
the
collector
of
H155
and
applied:
one
to
the
tape
out
jacks
through
monitor
‘switch
on
the
front
panel
and
the
other
to
the
function
rotary
switch,
Se:
:
The
DC
component
of
the
detected
1F
signal
is
used
as
a
AGC
voltage
to
control
emitter
current
of
H153
which
in
turn
control
the
bias
current
of
the
RF
amplifier
through
the
resistor
R179
and
R751.
A
part
of
IF
signal
output
is
also
applied
to
the
diode
H158
through
a
capacitor
C167
and
rectified
to
obtain
DC
current
for
energizing
the
AM
signa!
strength
meter
Mo01,