122
+23V
REPRODUCE
EOUALIZER
REPRODUCE
AMPLIFIER
HEAD
0101,0102
DOLBY
DECODER
0509
UIOI
LD
MONITOR
CIRCUIT
R660
0103
I
RI13
PINCH
ROLLER
0695
R
ch
SOLENOID
R213
L693
Fig. 3-24
Reproduce
muting circuit
3-10-2 Reproduce
muting
circuit
See
Fig. 3-24.
The reproduce
muting
circuit
mutes the repro-
duce equalizer
amplifier
to
prevent the genera-
tion
of
undesirable noise in modes other than
the reproduce mode.
1)
Muting
on
In a mode
other
than the reproduce mode
(stop mode,
for
example), the reproduce
muting
circuit
operates
as
follows
to
mute
the reproduce equalizer amplifier.
a.
In the stop mode, the pinch roller sole-
noid drive transistor
0509
is
off.
b.
Because
of
this
base
current
isnot
supplied
to
transistor
0614
and
it
remains
off.
c.
As
0614
is
off,
base
current
of
0113
flows
via path
CD
, therefore
it
is
on.
d.
As
0113
is
on,
base
current
of
0112
flows
via path ® and
it
is
on.
At
this
time,
capa-
citor
C 136
is
charged
to
+23
V.
e.
As
0112
is
on,
the
base
current
of
0103
flows via path @ and
it
is
on
so
the
reproduce equalizer
amplifier
is
muted.
Because
the signal level
is
low
in the
0103
circuit
its
collector
is
grounded
to
reduce
muting
transistor switching noise
..
2)
Muting
off
When pinch
roller
solenoid drive transistor
0509
turns
on
in the reproduce mode,
mut-
ing
is
released by the
following
process.
a.
As
0509
is
on,
base
current
is
applied
to
0614
and
it
turns on.
b.
As
0614
is
on,
0113
turns
off
as
its
base
current
CD
is
cut
off.
c.
When
0113
is
off,
the
base
current
@
applied
to
0112
is
cut
off.
0112
does
not
go
off
immediately
since C136's discharge
current
® flows
to
its
base.
d. As C136 discharges, its discharge
current
® (the
base
current
of
0112)
decreases
gradually, causing the
collector
current
of
0112
to
decrease gradually. Therefore, the
base
cu
rrent
of
0103
decreases
an
d
it
goes
off
grqdually.
0103
turns
off
approximately
400
msec
after
0509
is
turned on.
e.
Once
0112
turns
off,
the
base
of
0103
is
fixed
at a negative voltage applied through
R 150
to
lock
it
in the
off
state. Reproduce
muting
is
completely
released in this condi-
tion.
27
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