INTRODUCTION
This
service
manual
was
prepared
for
use
by
Authorized
Warranty
Stations
and
contains
service
information
for
the
Marantz
Model
2275
Stereophonic
Receiver.
Servicing
information
and
voltage
data
included
in
this
manual
are
intended
for
use
by
knowledgeable
and
experienced
personnel
only.
All
instructions
should
be
read
carefully.
No
attempt
should
be
made
to
proceed
without
a
good
understanding
of
the
operation
of
the
receiver.
The
parts
list
furnishes
information
by
which
replacement
parts
may
be
ordered
from
the
Marantz
Company.
A
simple
description
is
included
for
parts
which
can
usually
be
obtained
through
local
suppliers.
1.
SERVICE
NOTES
As
can
be
seen
from
the
circuit
diagram,
the
chassis
of
the
Model
2275
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.
LT.
EM
Front
Endl
cccsscsssssrsserceececcecccecesccceeceseeersesseaannececaeeessecescenssans
Mounted
on
P.W.
Board
P100
2.
FMIF
Amplifier
sssesseseescesssesesreeseeseeeeteenseennensessessaneneeseeteenees
Mounted
on
P.W.
Board
P200
3.
AM
Turner
Unit
cccescessececeeceeeeeeeceeceeseeeteeessseeseriseeesensensesseereeeressenees
Mounted
on
P.W.
Board
P150
4.
MPX
Stereo
Decoding
Amplifier
—
s:-:scessssesseseeseserereenes
Mounted
on
P.W.
Board
P300
5.
Phono
Amplifier
-:--ceeeccesccesseessreesesscestneeteessatstesetsenneseeesseenees
Mounted
on
P.W.
Board
P400
6.
Power
Amplifier
---::cesseseseeesessesseteseeseseneenetetsereeneeenseeaenees
Mounted
on
P.W.
Board
P700
7.
Power
Supply
and
Protection
Relay
Circuit
+--+:
Mounted
on
P.W.
Board
P800
8B.
Pre
and
Tone
Amplifier
-----::ss:seesesetetseeretteetertseesssereetessteaes
Mounted
on
P.W.
Board
PEO'
9.
Dolby
FM
Level
Amplifier
--:--:ss:ssessreceersteterteetretsstseesseresees
Mounted
on
P.W.
Board
PCO1
10.
Muting,
Speaker,
Loudness,
Power,
Hi
and
Low
Filter
SWITCHES
—
cceccceecccceresseeesceeeeceeeeetceesetsernssersuseansceanrncoseetans
Mounted
on
P.W.
Board
PTO!
11.
Dolby
FM,
Mono
L,
R,
Multipath,
and
Tape
Monitor
SWitChes
-vrvrsesscecsrceeeeecserececeeteecetensnsaeseneuenanenesecsaneeees
Mounted
on
P.W.
Board
PSO1
12.
FUMction
Lamps
cvvvsssrscesseseesesetsetsecseneesencsesenenerennassenstneecatneengs
Mounted
on
P.W.
Board
PY0O}1
13.
Dial
Larmps
-vvesssesessesseseessestenneeseeseneretteeenreseteesecncsnesreseaensesaeatees
Mounted
on
P.W.
Board
PZ01
14.
Muting
Level
and
Antenna
Attenuator
-erresrettreseescereees
Mounted
on
P.W.
Board
PUO'
2.
AM
TUNER
The
AM
Tuner
section
in
the
2275
consists
of
one
IC,
including
an
RF
amplifier,
local
oscillator,
mixer,
IF
amplifier,
and
detector,
and
three
transistors,
one
of
which
comprises
a
signal
strength
indication
amplifier
and
the
other
two
comprise
a
detected
audio
signa!
amplifier.
All
components
except
the
tuning
capacitor
and
ferrite
bar
antenna
are
mounted
on
the
printed
circuit
board
P150.
The
AM
signal
induced
in
the
ferrite
bar
antenna
is
fed
to
the
RF
amplifier
input
(Pin
(2)
and
amplified
to
the
level
required
for
overcoming
conversion
noise,
thus
giving
good
S/N
performance.
The
tuned
circuit
inserted
in
each
of
the
output
and
input
circuits
of
the
RF
amplifier
assures
very
high
image
and
spurious
rejection
performance.
The
amplified
and
selected
AM
signal
is
then
applied
to.
the
Mixer
input.
The
local
oscillator
voltage
is
injected
to
the
other
Mixer
input
(Pin
(@)
through
a
capacitor
C157.
Then,
both
AM
signal
and
local
oscillator
output
voltage
are
mixed
and
converted
into
the
455kHz
intermediate
frequency.
The
resulting
IF
signal
is
applied
to
the
IF
transformer
L153
consisting
of
one
ceramic
filter
and
two
tuned
circuits.
The
output
of
L153
is
fed
to
the
IF
amplifier
input
(Pin
@)
through
a
coupling
capacitor
C162
and
amplified
to
a
sufficient
level
to
drive
the
detector.
The
detected
audio
signal
derived
from
pin
@)
is
filtered
and
amplified,
and
the
final
audio
output
is
obtained
from
the
collector
of
H153
and
applied
to
the
TAPE
MONITOR
OUT
jacks
through
the
function
switch
S001.
The
DC
component
of
the
detected
IF
signal
is
used
as
an
AGC
voltage
to
control
the
emitter
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