Pioneer PX-7 Service Manual page 76

15.
RF
Modulator
The
RF
modulator
includes
the
following
blocks.
(1)
Buffer 5
and clamp
circuit
2
The
RF
modulator modulation
ratio
is
optimiz-
ed to ensure
that
the synchronization
destina-
tion voltage
of the video
signal
from
the video
output terminals
is
kept
at
OV.
(2)
Mixing/pre-emphasis
circuit
Conversion of audio
left
and
right channel
outputs to
monaural
by
mixing
circuit,
and
performing pre
emphasis by
emphasizing the
high frequency components.
(3)
Limiter
The
audio output
level
is
limited to prevent
over modulation of the
RF
modulator.
B.
Audio
Signal Circuits
1.
Buffer
6 and Buffer 7
Buffer
amplifier for conversion
of the audio
input impedance.
2.
Low-pass
Filters
1
&
2
12dB/oct low-pass
filters
{fo
= 16kHz)
for
audio
signals
from
PSG (YM-2149) and PPI
(8255)
in
the
CPU
ass'y.
3.
L
&
R
Muting
External audio
signal
muting
circuits
for
inde-
pendent
left
and
right
channel muting.
4.
L
& R
Mixing Circuits
Adder
circuits
using operational
amplifiers
for
mixing the
external
audio
and
ASC
(PSG,
PPI,
SOUND
IN)
signals.
5.
Power Amplifiers
1
&
2
Amplification of the
mixed
left
and
right
channel audio
signals
to speaker and headphone
driver
levels.
C.
Through
Switch Circuits
1.
Through
Relay
Switching relay for
output
of external video and
audio
signals
applied to the
VIDEO
and
AUDIO
INPUT
terminals direct to
the
VIDEO
and
AUDIO
OUTPUT
terminals (through) or input
to the
ass'y
processing
circuits
(normal).
The
relay consists of
two
plungers
PM1
and
PM2,
and
relay switches
RY102-(l/8)
thru
(8/8)
in
an
integrated device.
2.
Driver Circuit
Driver
circuit
used to
activate
the through
relay
plungers
PM1
and
PM2
to switch
RY102.
3.
Charge
Storage
Circuit
This
circuit
supplies the
power
to
drive plungers
PM1
and PM2.
4.
Switch
Position Detector
This detector
circuit
checks
that the relay
switch
has
been
properly switched by
plunger
action,
and
feeds the
result
back
to the pulse generator
circuit.
5.
Pulse
Generator
Generation of
pulse
signals
to
be
passed to the
driver
circuit
to drive
plunger
PM1
or
PM2
on
the
basis
of information
received
from
the
timing
circuit
and
the switch
position detector.
6.
Timing
Circuit
This timing
circuit
is
involved in setting
the
switching timing
for
the through
switch,
and
passing
a
trigger to the
pulse generator.
7.
Rectifier
Generation of
voltage for switching the timing
circuit
on
and
off.
8.
Regulator
Supply of
power
to
the timing
circuit
and
pulse
generator.
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