Technics ST-9038 Manual page 16

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