Marantz 2220 - Page 4

into
the
base
of
Mixer
transistor,
the
injection
voltage
is
about
50mV.
The
10.7MHz
front
end
IF
output
is
led
to
the
next
IF
amplifier
unit
through
a
coaxial
cable.
oo
The
IF
amplifier
unit
consists
of
five
stages
of
IF
amplifiers.
Two
pieces
of
ceramic
filters
are
used
to
obtain
high
selectivity
a
pair
of
symmetrical
diode
limiter
is
also
employed
for
the
best
limiting
characteristics,
improved
cdpture
ratio
and
good
AM
suppression.
A
part
of
IF
amplifier
H202
is
rectified
by
the
diodes
H210
and
H211
and
its
DC
output
is
fed
back
to
the
gate
of
FET
RF
amplifier
to
decrease
the gain
of
it
with
increased
input
signal
strength.
3-1 Muting and Auto-Stereo Switching Circuits
The
muting
circuit
consisting
of
all
solid-state
electrical
switching
has
been
incorporated
in
the
Model
2220.
The
DC
voltage
obtained
by
rectifing
a
part
of
IF
output
signal
from
the
H204
is
applied
to
the
base
of
H207
and
turns
on
it
if
the
IF
output
is
greater
than
predetermined
level
(muting
threshold
level).
When
the
H207
is
turned
on,
the
H208
is
turned
off,
thus
allowing
the
emitter-collector
resistance
of
the
H208
increasing
and
the
collector
voltage
rises
about
8V.
The
increased
collector
voltage
increases
the
base
bias
voltage
and
makes
the
switching
transistor
H209
turn
on,
thus
decreasing
the
collector-emitter
resistance
to
near zero
ohm
and
allowing
the
power
supply
path
to
the
H205
closed.
When
the
input
signal
is
lower
than
the
predetermined
level,
the
DC
output
obtained
is
small
and
can
not
turn
on
the
H207,
thus
the
H207
keeps
its
turn-off
state
and
this
makes
H208
turn
on,
decreasing
the
collector
voltage
and
turning
off
H209.
Thus
no
power
is
supplied
to
the
H205
and
signals
below
the
threshold
level
are
muted
out.
The
muting
threshold
level
can
be
varied
by
adjusting
the
trimming
resistor
R245.
The
DC
voltage
developed
at
the
collector
of
H208
is
also
used
to
make
the
Auto-Stereo
switching
transistor
H304
turn
on
and
off.
3-2: MPX Stereo Decoding Circuit
Non-equalized
audio
signals
are
applied
to
the
first
amplifier
H301
which
serves
as
a
tuned
amplifier
for
the
pilot
signal
in
the
composite
signals
and
as
a
buffer
amplifier
for
the
rest
audio
signals.
The
amplified
19KHz
pilot
signal
is
led
to
the
second
19KHz
amplifier
H302
and
further
amplified
if
switching
transistor
H304
is
turned
on
by
the
controlling
DC
signal
as
described
above.
The
19KHz
pilot
signal
is
rectified
by
the
doubler
circuit
consisting
of
H312
and
H313
to
obtain
synchronized
38KHz
signal
to
drive
the
H303.
The
H363
is
the
38KHz
tuned
amplifier
and
supplies
its
output
to
the
switching
matrix
circuit
consisting
of
four
diodes.
The
composite
signals
are
applied
to
the
center
tap
of
switching
transformer
L304
and
decoded
into
left
and
right
channel
signals,
then
both
channel
signals
are
led
to
the
crosstalk
cancelling
amplifier
which
utilizes
complementary
confuguration
with
NPN
and
PNP
transistors
through
de-
emphasiss
networks.
Transistors
H310
and
H311
are
buffer
amplifiers
and
their
outputs
are
led
to
the
function
switch.
.
3.3 Suggestion for Trouble Shooting of FM Tuner
3.3.1 Symptom: No FM Reception
First
turn
ON
the
power
switch
and
try
to
tune
FM
stations.
Rotate
the
fly-wheel
tuning
knob
slowly
and
observe
the
FM
tuning
meter.
If
the
meter
deflect
at
several
frequencies
received,
the
circuits
preceding
the
IF
amplifier
H204
may
have
no
failure.
When
no
reading
is
obtained
in
the
meter,
check
FM
local
oscillator
circuit,
using
a
RF
VTVM.
The
normal
local
oscillator
voltage
is
one
or
two
volts
(rms)
at
the
tuning
capacitor,
depending
on
the
tuning
capacitor
position.
if
the
local
oscillator
voltage
is
normal,
next
check
all
voltage
distributions
in
the
FM
circuits
and
compare
them
with
those
shown
in
the
circuit
diagram.
When
the
tuning
meter
deflects
aut
no
sound
is
obtained,
check
audio
circuits,
using
a
ans
sensitive
oscilloscope.