Marantz 2220B - AM Tuner; AM Tuner Operation; AM Tuner Troubleshooting

INTRODUCTION
This
service
manual
was
prepared
for
use
by
Authorized
Warranty
Stations
and
contains
service
information
for
Marantz
Model
2220B
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
part
lists
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
2220B
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 Front End & AM Tuner... ..... 0c eee ee eee mounted on P.W.B. P100
2.
FMIF
Amplifier,
Detector,
Muting
Control
..............
mounted
on
P.W.B.
P200
3.
MPX
Stereo
Decoding
Amplifier
.......
0...
cee
eee
eee
mounted
on
P.W.B.
P300
4. Phono Amplifier .. 0... 0... ce es mounted on P.W.B. P400
5.
Tone
Amplifier
....
0.0...
ce
cc
eee
eens
mounted
on
P.W.B.
PEO1
6.
TAPE
Montor,
Mono,
Low
and
High
Filter
Switch
Unit
.....
mounted
on
P.W.B.
PHO!
7.
Loudness,
Muting,
Main
and
Remote
Switch
Unit
.........
mounted
on
P.W.B.
PTQO1
8.
Power
Amplifier
..
0.0.0.0...
ccc
ee
ee
ees
mounted
on
P.W.B.
P700
9.
Power
Supply
......
0.
cece
eee
ce
eee
eee
eee
eens
mounted
on
P.W.B.
P800
10.
Dial
Lamp
Unit
2...
...
0
cc
eee
ee
eens
mounted
on
P.W.B.
PZ0O1
2. AM TUNER
All components except ferrite bar antenna are mounted on a printed circuit board P100.
The
AM
signals
induced
in
a
ferrite
bar
antenna
are
applied
to
the
RF
amplifier
section
of
’ the AM tuner IC H104 through a capacitor of C129 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
converter
section
through
a
coupling
capacitor
C132.
While
the
local
oscillator
voltage
is
injected
through
a
capacitor
C131,
both
AM
signals
and
oscillating
voltage
are
mixed
and
converted
into
455K
Hz
intermediate
frequency.
The
resulting
IF
signal
is
applied
to
the
first
IF
transformer
L110
consisting
of
one
ceramic
filter
and
two
tuned
circuits.
The
output
of
L110
is
led
to
the
IF
amplifier/detector
section
of
H104.
The
detected
audio
signal
is
obtained
from
PIN
11
of
H104
and
amplified
to
a
required
level
(about
470
mV
far
400Hz
30% mod.)
by
the amplifier
H105 and
fed
to
the
function
switch.
2.1
Suggestions
for
AM
Tuner
Trouble
Shooting
Check
for
broken
AM
bar
antenna,
next
connect
an
oscilloscope
to
the
pin
11
of
H184
0
J112 and
check
for
audio
signals
with
the tuning
meter
deflected.
If detected
audio signal
is
obtained
at pin
11
of
H104,
no
failure
may
exist
in the
AM tuner
IC
H104
and
its
associate¢
circuit.
If
no
audio
signal is
obtained
at
pin
11
of
H104,
check
all
voltage
distribution
in
ths
AM
circuits by
using a DC
VTVM.
3. FM TUNER
The
FM
Tuner
section
of
Model
2220B
is
divided
into
three
functional
blocks:
FM
fron
end, IF amplifier & Detector, Muting control and MPX stereo decoding circuit.