Marantz 4270 - Marantz 4270 Phono and Pre-Amplifier

Peat: Bot: Bt we 4
thereby
avoiding
a
wrong
stereo
operation.
H303
attached
on
the
outside
of
pin
@)
is
a
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
is
grounded,
thereby
developing
a
condition
for
monaural
reception.
For
a
forced
monaural
operation,
switch
the
MODE
switch to
“MONO,”
and
H303
comes
into an
“On” condition
with
the
positive
bias
voltage
applied
to
the
base,
and
pin
is grounded,
thereby
establishing
monaural
operation.
The
transistor
H302
connected
externally
to
pin
(4
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
(4
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
signal
strength
meter.
!f
the
signal
strength
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
(rms)
at
the
tuning
capacitor,
depending
on
the
tuning
capacitor
position.
If
the
local
oscillator
voltage
is
normal,
next
check
all
voltage
distribution
in
the
FM
Front
End
and
IF
amplifier
unit
and
compare
them
with
those
shown
in
the
circuit
diagram.
When
signal
strength
meter
deflects
but
no
sound
is
obtained,
check
audio
circuits,
using
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
(J310)
using
an
oscilloscope
and
a
frequency
counter.
,
4. PHONO AND PRE-AMPLIFIER
Signals
from
the
PHONO
jacks
are
applied
to
the
phono
amplifier
mounted
on
P400.
The
amplified
and
RIAA
equalized
phono
signals
and
signals
from
the
tuner
section,
CD-4/AUX
and
TAPE
MONITOR
IN
jacks
are
applied
to
the
SELECTOR
switch
which,
in
turn,
leads
the
selected
signals
to
the
TAPE
MONITOR
OUT
jacks
and
MODE
switch.
Applied
to
the
other
section
of
the
TAPE
MON
switch
are
signals
from
the
TAPE
MONITOR
IN
jacks.
The
TAPE
MON
switch
selects
the
signals
from
the
MODE
switch
or
those
from
the
TAPE
MONITOR
IN
jacks
and
the
selected
signals
go
to
the
DOLBY
and
MODE
switches.
Signals
are
then
mode
processed
by
the
MODE
switch
and
its
associated
circuit
and
applied
to
the
tone
control
amplifier
through
the
buffer
amplifier
and
BALANCE
and
VOLUME
controls.
The
bass
mid
and
treble
controlled
signals
from
the
tone
contro!
amplifier
pass
through
the
hi-filter
before
they
reach
the
main amplifier.
4.1 Mode Switch
MODE
switch
S002
has
positions
of
MONO,
2
CH,
DISCRETE,
VARI-MATRIX,
and
SO
DECODER.
In
the
MONO
position,
all
input
signals
are
mixed
together
and
delivered
to
all
four
channels.
In
the
2
CH
position,
each
pair
of
input
signals
right-front
(RF)
and
right-rear
(RR),
and
left-front
(LF)
and
left-rear
(LR)
are
mixed
together.
The
resultant
signals
(RF
+
RR)
and
(LF
+
LR)
are
delivered
to
the
pairs
of
RF
and
RR,
and
LF
and
LR
channels,
respectively.
In
the
DISCRETE
position,
each
channel
signal
is
separately
routed
to
the
corresponding
channel.