Akai AP-207

a
pulse.
The
reset
pulse
of
20
Hz
for
33-1/3
rpm
or
27
Hz
for
45
rpm
shaped
from
the
FG
signal
is
compared
with
the
above-mentioned
set
pulse
entering
ICS
@,
and
the
output
appears
at
ICS
@.
The
output
pulse
is
smoothed
by
the
low-pass
filter,
consisting
of
C9,
C10
and
R5
through
R7,
and
enters
IC5
@),
then
the
inverted
output
is
fed
from
IC5
@.
The
output
of
ICS
@
fed
through
R8
and
SW903
to
IC1
@),
in
the
D.D
circuit
as
the
reference
voltage.
In
short,
when
the
Quartz
Lock
Switch
SW903
is
off,
the
reference
voltage
is
made
of
the
+B
voltage,
while
when
it
is
on,
the
pulse
made
of
the
FG
signal
is
compared
with
the
pulse
generated
by
the
crystal
oscillator
to
produce
the
reference
voltage.
The
succeeding
operation
is
similar
to
the
one
when
the
Quartz
Lock
Switch
is
off.
3. STROBE LIGHT CIRCUIT
(Refer
to
the
PLL
Circuit
schematic
diagram
of
the
AP-307)
The
4.42368
MHz
signal
generated
by
the
crystal
oscillator
is
delivered
through
TP-1
to
IC2
@).
The
Flip-Flop
in
IC2
halves
the
oscillation
frequency
to
2.21184
MHz.
The
halved
signal
is
fed
from
IC2
@,
to
IC3
@®.
IC3
counts
the
frequency
down
to
1/27
for 33-1/3 rpm or 1/20 for 45 rpm.
The
count-down
signal
is
fed
from
IC3
10,
to
IC4
®@.
IC4
further
counts
the
signal
down
to
160
Hz
at
IC4
@
,
320
Hz
at
IC4
@
and
80
Hz
at
IC4
@
for
33-1/3
rpm
or
to
216
Hz,
432
Hz
and
108
Hz
for
45
rpm,
respectively.
These
output
signals
are
input
to
the
NOR
circuit
of
IC6
(1
to
5).
The
NOR
circuit
outputs
from
IC6
@,
80
Hz
signal
for
33-1/3
rpm
or
108
Hz
signal
for
45
rpm.
The
signal
is
fed
through
R10
to
TRI
to
turn
on
and
off,
which
flashes
the
neon
lamp
NE901.
Reference:
Logic
Symbols
and
Their
Truth
Table