Circuit Composition - Pioneer QX-949A Series Service Manual

Circuit Composition
Three ICs are employed, as shown
in
Fig. lb.
M5165LP is an SQ basic decoder and can function
€rs
an
SQ
decoder
without
independent
logic.
Although a
phase
shift
network is
not
included,
by a
CR network, this IC perform
to
shift
the
phase
90' with
cover wide
range.
A
selector switch
also permits
the IC to
be used
as
an RM
decoder.
During RM, a
blend resistor is
added
at
the front,
while the
rear is blended internally
by the IC
and
taken from
separate
terminals.
CX.049 is
a
high density
full
logic IC incorporating
both
wave
matching and
front
back logic. CX-718D
is a
gain control IC
and contains
four
MOS FETs
to form
a
variable resistance voltage
control circuit.
Since these
MOS FETs
are P
channel enhancement
types, equivalent internal
resistance becomes in-
finite
when gate voltage
is
zero.
By
applying
a
negative voltage to the
gate
(Fig.!4),
the equivalent
internal
resistance
can be varied
from infinity
to
several
hundred
ohms.
r---
-_J
Basic
decoder
GIX-g4slA
2SK40V
(FET)
is
employed
for
back blending.
With a
CF
sound source,
it
functions
to
cancel
the mutually opposite
crosstalk phase
to
LB
and
RB. This is an N
channel depletion type junction
FET
and
when the
gate
voltage
is
zero) the channel
is
already established.
LB and RB become normally
blended
for
this reason, and the
gate becomes
open
only in the
case
of
a
single signal
from LB or
RB.
10
7
l0
6
Rn.
(s2
)
10,
l0 3
10,
-l
-2
Y6s(v
)
Fis.
14
u----l
tull
logic
r---
-----1
I
i
cx"7l
8D
iti
iHi
Time constant circuit
F
is.
15