Technics ST-9038

i
CIRCUIT
FOR STARTSANÞ
STOP
PULSE
GENERATION
ENT CIRCUITS
PART
II
IN AUTO
TUNING AND
ADJAC
I
2-1-3 Stop
pulse generat¡on
When
the AT
button
is not
pushed
in the
circuit
ment¡oned in2-1-2, TF910
is
biased
via R941 and
turned
on.
With the button
pushed,
however,
the TR910
base
is clamped
to
ground
at
D920
(O499)
and
turned off. At
that
time,
the collector
potential
changes
as follows:
Change
in
potential
of TR910
collector
+B
AT
button
Pushed
AT
button
released
+B
,,H,
It
passes
through C916
and C915.
Also,
pin@of
1C912
is connected
to
+B
line
at R939,
therefore
the wave
form as
shown
below
will be
generated.
At
that
time, the
pulse
level
at
changes
from
t
o
1
1
"H"
ro
"L".
So,
pins
@
and
by
putting
the
pulse
into
pin
can be inverted
shown in the
TR91O
collector
1c912
pin
@
o "L"
O"L
+B
,,H,,
aforementioned
f lip-f
lop cirucuit.
(Stop
pulse).
The above operations
occur
in the case of step-
scan.
ln auto tuning
(standard
or fine), however,
the
TR910 collector
is
grounded
bV S2-2 and
no
pulse
is
generated.
The stop
pulse
in auto tuning is
generated
at TR109.
(A
description
is
given
separately.)
\+
t
t
2-1-4 Adjacentcircuits
Description of the muting control.
When the local oscillator is
fluctuating
during
auto
tuning or step scan,
noise
or
impulse sounds
would
be
mixed
with
the regular signal.
Therefore,
the output signal is
cut
off by using
the muting
f unction
during
auto
tuning
The control signal
prn
@
of rcg12 is used for muting. The descriptions
given
in 2-1-1
,
2-1-2 and
2-1-3 can
be
summarized
and figured
as
follows:
(during
step scan)
AT button
pushed
AT button
released
lcel2
pin
@
(Start
pulse
¡nput
pin)
lce12
pin
@
(Stop
pulse
input
pin)
rcel2pin@t@l
(Mut¡ng
c¡rcuít
control
signal)
rcel2pin
@
t@l
(To
clock
OSC
sect¡on)
H
L
H
L
H
L
H
L
-14-
Q