Circuit Description; Muting Circuit; Mpx Decoder Circuit; Pulse Noise - Pioneer TX-9100 KUW Service Manual

TX-91clcl
5.
CIRCUIT
DESCRIPTION
5.1
MUTING
CIRCU IT
The block
diagram
in
Fig.
1
shows
rF
sTGNAL
the
basic
function of
this circuit.
The
signal
path
is grounded
when
the
relay
contacts
are closed.
Synchronizes
timing
of
audio signal with
that of
noise
suppres-
sion pulse.
Signal
level
is
maintained
constant
during
OU T
PUT
Fis.
1
STEREO
INDICATOR
LAMP
Fig.2
Fis.
3
9
I'/U
T
ING
SWI
TCH
5.2
MPX
DECODER
CIRCUIT
The MPX
decoder
is a
radically
new
design operating
on the PLL
(phase
locked loop) principle; it
has
no
capacitances
or
induct-
ances.
Its function
is
evident from
the block
diagram
in
Fig.
2.
VCO
stands
for
Voltage
Control
Oscillator its
oscillation
fre-
quency varies with the
supplied
input
voltage.
Adjust
the
free-
running
frequency control
so
that
the
frequency
becomes 76kHz
(19kHz
at
the TP terminal)
when
no
signal
is
present.
5.3
PU
LSE
NOISE
SUPPRESSOR
The
Pulse Noise Suppressor (PNS)
circuit
is
included
to
eliminate
pulse-type noise
signals
as caused
by
automobile ignitions etc.
Fig.3
shows
the block
diagram
of
this
circuit.
The circuit
is so
designed
that
it
will not
function
when
a
very weak signal with
considerable
inherent
noise
is being received.
CO
MPOS ITE
SIGNAL
No output
when phase
dif
ference
in input is
90"
AUDIO SIGNAL
Oscillation frequency
changes
so that phase relation to
input signal becomes gO"
SCHMITT
CIRCUIT
SCHMITT
CIRCUIT
IF
SIGNAL
lo,o,o
,l
OUTPUT
norse
suppresslon,
by
integrated
circu it.
TECTO
tc
Ic
--l
f--
DIFFE.
RENTIAL
I r-IAMP
&
I
i
lsrrqsrruc
rr
CIRCUIT
DC potentiai
when
DC
VOLTAGE
SENSOR
NOISE
LEVEL
SENSOR
y'
nrr-nv
PHASE
COMPA
ATOR
vc0
(76kHz)
fx
1/2
(38kHz)
ad
iustment
SWITCHING
SIGNAL
(38kHz)
OMPARATOR
DEIVODU-
LATO
R
Stops
noise
suppres-
sion pulse when
input
Y,il;|Sxfu ;L'll!
r'?il
G
ENERATES
NO
ISE
SUPPRESS ION
PULSE.
/
GATE
CIRCUIT
EVEL
ENSOR
FILTER,
AUDIO
AMP