Marantz 2220B - FM Tuner; FM Reception Troubleshooting; Phono and Pre-Amplifier

DIV-1
and
DIV-2,
and
the
19KHz
pilot
signal
included
in
the
stereo
composite
signal
as
a
reference
signal
is
applied
to
the
other
input.
Therefore,
the
output
of
PD-1
which
has
passed
through
the
low
pass
filter
LPF-1
provides
DC
output
voltage
in
proportion
to
the
phase
variance
between
the
two
inputs.
This
DC
output
voltage
is
amplified
by
the
DC
amplifier,
and
supplied
to
the
76KHz
VCO
as
a
contro!
voltage.
This
means
that
the
output
frequency
and
phase
of
the
VCO
have
been
phase-locked
to
the
input
pilot
signal.
The
38KHz
sub-carrier
reproduced
by
PLL
as
stated
above
is
delivered
through
the
stereo
switch
to
the
stereo
decoder
section
as
a
switching
signal,
thus
driving
the
decoder
section.
One
of
the
inputs
of
PD-2
is
given
the
19KHz
resulting
from
the
frequency
division
completed
by
DIV-1
and
DIV-3,
whereas
the
other
input
gets
the
19KHz
output
contained
in
the
composite
signal,
and
the
output
is
provided
with
a
DC
output
in
proportion
to
the
amplitude
of
the
pilot
signal.
This
DC
output
is
furnished
through
LPF-2
to
the
trigger
amplifier
which
drives
the
stereo
indicator
lamp
and
stereo
switch.
Therefore,
insufficient
supply
of
the
pilot
signal
results
in
failure
to
light
the
stereo
indicator
and
to
turn
on
the
stereo
switch
located
in
the
path
of
the
38KHz
switching
signal,
thereby
avoiding
a
wrong
stereo
operation.
H303
attached
on
the
outside
of
pin
8
isa
switching
transistor
for
automatic
monaural-stereo
switchover.
When
the
intensity
of
an
incoming
signal
from
an
FM
station
is
weaker
than
a
predetermined
level,
this
H303
is
turned
on
and
pin
8
is
grounded,
thereby
developing
a
condition
for
monaural
reception.
For
a
forced
monaural
operation,
switch
the
MODE
switch
to
“NONO,”
an
H303
comes
into
an
“On”
condition
with
the
positive
bias
voltage
applied
to
the
base,
and
pin
8
is
grounded,
thereby
establishing
monaural
operation.
The
transistor
H302
connected
externally
to
pin
14
is
intended
to
stop
the
76KHz
oscillation
of
the
VCO
Which
interferes
an
AM
signal
during
the
reception
of
an
AM
station.
When
the
function
switch
is
set
to
‘“AM”
position,
a
positive
bias
is
charged
on
the
base
of
H302,
H302
is
turned
on,
and
pin
14
is
grounded.
Thus,
the
oscillation
of
the
VCO
is
stopped,
ending
the
interference
with
AM
reception.
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.
lf
the
turning
meter
deflect
at
several
frequencies
received,
the
tuner
circuits
preceding
the
discriminator
circuit
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
(fms)
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
Front
End
and
IF
amplifier
unit
and
compare
them
with
those
shown
in
the
circuit
diagram.
When
the
tuning
meter
deflects
but
no
sound
is
obtained,
check
audio
circuits,
using
a
high
sensitive
oscilloscope.
3.3.2
Symptom:
No
Stereo
Separation
First
check
the
“MONO”
switch
is
in
normal
out
position.
Connect
a
FM
RF
signal
generator
output
modulated
by
a
stereo
modulator
to
the
rear
FM
antenna
terminals,
and
check
the
stereo
beacon
is
turned
on
or
not.
If
not
turned
on,
check
for
19KHz
VCO
output
signal
(R312
Test
Point),
using
an
oscilloscope
and
a
frequency
counter.
4.
PHONO
AND
PRE-AMPLIFIER
Signals
from
the
tuner
and
AUX
jacks
are
applied
to
the
selector
switch.
Signals
from
the
PHONO
jacks
are
applied
to
the
phono-amplifier
consisting
of
transistor
H401,
H403
and
H405.
The
gain
of
the
amplifier
is
40
dB.
The
amplified
and
equalized
phono-signals
are,
then,
fed
to
other
section
of
the
selector
switch
which,
in
turn,
applies
output
signals
from
the
tuner,
phono-amplifier
and
AUX
jacks
to
the
TAPE
1
MONITOR
switch
and
TAPE
OUT
1
jacks.
The
TAPE
1
MONITOR
switch
applies
the
signals
to
the
balance
and
volume
controls.
The
controlled
signals
are
fed
to
the
pre-amplifier
consisting
of
HEO1,
HEO3
and
HEOS,