Technics QUARTZ SL-MA1 - Page 13

SL-MA
1. Power supply control circuit
DC
input
-¢
~
12V
z
iid
a4
o—
5V
+
om
.
4
©
vt
Qo
+
+
-
+»
GND
¢
Power ‘‘on’’ at L
Power “‘off’’ at H
S601 "on"
H S60!
| | a Power
l
With
the
AC
cord
connected
to
a
power
outlet
socket,
a
voltage
is
generated
at
point
@),
and
then
over
0.6V
is
applied
to
the
base
of
Q1
to
turn
it
on.
As
Q1
is
turned
on,
the
base
of
Q1
is
nearly
at
ground
potential
causing
Q2
to
turn
off
and
then
no
output voltage is generated. (initial condition)
When
$601
(power
switch)
is
turned
on,
the
voltage
at
point
is
clamped
at
about
0.6V,
and
the
base
voltage
of
C11
be-
comes
lower
than
0.6V,
then
Q1
turns
off.
As
Q1
is
off,
the
base
voltage
is
applied
to
Q2
to
turn
it
on.
Thus,
Q3
and
O4
are
operated
to
supply
power
of 12V
and
5V.
The
5V
power
supply
causes
the
microcomputer
to
operate,
then
the
level
of
terminal
@5)
becomes
becomes
“’L’’
arnd
the
voltage
at
point
is
lowered
to
the
ground
potential
through
Q405,
thereby
holding
Q1
in
an
‘‘off”
state.
With
S601
(power
switch)
again
turned
on,
the
pulse
rising
at
the
moment
when
the
switch
is
released
is
input
to
terminal
of
the
microcomputer,
then
the
level
of
terminal
(2)
becomes
'‘H’’,
Q405
turns
off,
the
potential
at
point
becomeshigher,
Q1
turns
on,
and
delivery
of
output
voltage
is
discontinued.
Note:
Terminal
@)
of
microcomputer
is
provided
with
a
safety
function
to
shift
the
arm
back
to
the
rest
and
to
make
the
level
“H”
after
cueing
down
for
the
protection
of
stylus
tip
when
the
arm
is
not
on
the
rest.
2.
Auto
size
detection
circuit
1C401
(Inside)
*8
The
2
LED’s
light
up
with
180°
phase
shifted
pulses
of
pin
and
pin
Q)
of
microcomputer
(1C401)
and
are
fitted
On
the
inner
and
outer
periphery
sides
of
turntable
platter.
On
the
inner
periphery
side,
the
light
is
received
through
prism,
and
on
the
outer
periphery
side,
directly
by
photo
transistor
(PTR501).
The
light
received
is
input
to
pin
through
the
filter
amplifier
and
wave
shaping
circuit.