122
3-10-3 Record
muting
circuit
See
Fig. 3-25.
Record
inhibit
switch S694 operates by mechani-
cally detecting the presence or
absence
of
a
re-
cord
protection
tab on the cassette loaded in the
deck.
S694
is
in the N.O. position
if
the loaded
cas
-
sette
is
protected
by
the tab being removed. In
this
case,
pin 9
(AR
IN)
of
system
control
IC
U601
is
fixed
at L level. The deck
will
not
enter
the record/reproduce mode when the P
LAY
and
RECORD
buttons
are
depressed simultaneous-
ly
if
terminal
AR
is
at L level. (The reproduce
mode
will
be enabled in this
case.)
S694 switches
to
N.C. when a recording-enabled
cassette tape (i.e.
protection
tab
not
removed)
is
loaded.
Now
current
from
U601 charges capa-
citor
C607 and terminal AR switches
to
H level.
When terminal
AR
is
at H level, recording
can
occur. Hereafter
it
is
assumed
that
terminal
A R
is
at H level.
1)
Record/reproduce mode
When the deck
is
in the stop mode, the cir-
cuits shown in Fig. 3-25
are
in the
following
conditions.
Pins 12 and 10
of
U601 : L level
Transistors: Q604, Q609, Q612, Q114, and
Q115:
off
Transistors: Q608, Q610, Q611,
Qll0,
and
Qll1:
on
Record
muting
Q116:
on
Record
muting
flip-flop:
reset
Bias oscillator
U103:
not
oscillating
If
the
PLAY
(
~
) and R ECOR D
buttons
have
been
depressed simultaneously, H-Ievel
signals
are
output
from
pins 12 and 10
of
U601. The reproduce mode signal
output
from
pin 12
is
mainly
for
the
control
of
mechan ical tape transport operations
(see
3-9-1). The record mode signal
output
from
pin 10 in itiates the
fol/owing
operations.
a.
When
an
H-Ievel signal
is
output
from
pin
10
of
U601,
base
current
floll\>3
through
Q604
and
it
turns on.
As
Q604
is
on, cur-
rent flows
through
the
RECORD
LED
and turns
it
on.
At
the
same
time,
Q611
turns
off
as
its
base
current
is
cut
off.
b.
As Q611
is
off,
Q610
turns
off
as
its
base
current
i,s
cut
off.
Similarly
Qlll
turns
off,
as
its
base
current
is
cut
off.
c.
As Q
111
is
off,
discharge
current
from
C 135 flows through the
loop
consisting
of
C135, the
emitter
of
Qll0,
the
base
of
Qll0,
and C135.
As
the discharging
of
C135 proceeds, the discharging
current
(the
base
current
of
Q 110) decreases and Q 110
turns
off
slowly.
d.
As
Q
11
0 turns
off
gradually,
the
base
cllr-
rent
of
Q 116 decreases gradua lIy and
it
is
turned
off
slowly. As a result, the record
amplifier
is
smoothly
released
from
muting.
e.
On
the
other hand,
if
an
H-Ievel signal
is
output
from
pin
10
of
U601,
base
current
flows
through Q 115 and
it
turns
on. There-
fore,
base
current
is
applied
to
Q114
turn-
ing
it
on.
f. When
Q114
has
turned on, bias oscillator
Q103 begins
to
oscillate, its
output
being
delivered
to
the
erase
head.
At
the
same
time,
it
is
added
to
the
output
Signal
(audio
signal)
from
the record
amplifier
after
its
level
has
been
adjusted
by
·the bias adjust
circuit
and the resulting signal
is
supplied
to
the record head.
2)
REC/MUTE
mode
If
you
depress the R
EC
MUTE
button
when
the
deck
is
in the
record/
rreproduce mode, the
recording signal
is
muted
to
leave
a blank
section
on
the tape.
When the deck
is
in
the
record/reproduce
mode
the
circuits shown in Fig. 3-25
are
as
in the
following
condition.
Pins 12 and
10
of
U601:
H level
Transistors: Q604, Q608, Q114, and
Ql15:
on
Transistors:
Q609-Q612,
Qll0,
Qll1,
and
Q116:
off
REC
MUTE
flip-flop:
reset
Bias oscillator: oscillating
Record
muting:
released
If
the
REC
MUTE
button
h
as
been depressed
in the record/reproduce mode, the circuits
operate
as
described below
to
enable the
REC/MUTE
mode.
a.
When
the
REC/MUTE
button
has
been de-
pressed, the REC
MUTE
flip-flop
is
reset
by
an
L-Ievel signal. Q608
turns
off
as
its
base
current
is
cut
off.
b.
As
Q608
is
off,
its col/ector
rises
to
H level
and
base
current
flows through
Q609
turning
it
on. When Q609
is
on, its col'lec-
tor
is
at
L level. Therefore,
if
the
REC
MUTE
button
is
released and the L-Ievel
signal
is
removed
from
the R
EC
MUTE
flip-flop,
Q608
stays
off
and
Q609
on.
c.
As
Q609
is
on,
base
current
flows
through
Q610,
turning
it
on. When
Q610
turns on,
Qlll,
Qll0,
and
Ql16
turn
on in sequ-
ence,
as
opposed
to
on in the record/
reproduce mode, and the record
amplifier
28
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