Pioneer TX-520 - Block Diagram; Circuit Descriptions; FM Multiplex Stereo Decoder; AM Tuner

3. BLOCK
DIAGRAM
FI
tooo
AM
TUNER
FM
IF AMP
A
OETECTOR
I
75n
GilO
(
FT,|
MPX STEREO
OEIT|oOULAIOR
Ic(HAil56wl
INOICATORS
Ftl
+B
+--i-
V.R.
+8
AM + B
---:o
I
4.
CIRCUIT
DESCRIPTIONS
FM Tuner
The
FM
front
end
is comprised
of
a
J-FET
(2SK168)
single+tate
RF
amplifier,
an
NPN
transistor
mixer,
and
an NPN
transistor
modified
Clapp local
oscillator.
The IF
stage consists
of
2
dualclement
ceramic
filters,
a single
transistor
amplifrer
element,
and an
IF
system IC
(PA3001-A)
which
incorporates
the
IF limiter
amplifier,
FM
detector,
and the
FM
muting
circuit.
FM
Multiplex
Stereo
Decoder
The
stereo
decoder
stage
employs
an
FM
MpX
IC
(HA1156W-P),
while
the subcarrier
signals
(frequencies
above
l9kHz)
are
removed
by an
-18d8/oct.
active
filter
consisting
of a
pNp
transistor.
This
active
filter
also
sewes
as
an
amplifier
for
frequencies
within
its
passband,
and
eliminates
crosstalk.
FM
IF SYSTEM
Ic
(PA300r-a
)
AM Tuner
This
employs
a
2-ganged
tuning
capacitor,
a
dualclement
ceramic
filter,
and
an
IC
(HA119T)
consisting
of
a RF
amplifier,
mixer,
2-stage
IF
amplifier,
detector
and AGC
circuit.
Signal
Strength
lndicator
The
TX-520
signal
strength
meter
is a
b-point
LED
display
meter
driven
by
the
meter
drive
IC
(L81416).
The signal
meter
drive
signals
from
the
FM
and
AM
tuner
sections
are
applied
to
a
set
of
5
voltage
comparators
which
are activated
according
to
the
difference
between
the
applied
signal
level
and
the
respective
reference
vottage
levels
allotted
to
each
comparator,
resulting
in
the
LEDs(1-5)
being
lighted.
METER
DRIVE
IC
(
L81416
)
Fig.
4-1
Signal
indicator
circuit