Circuit - Pioneer PL-200 Service Manual

7.5
OPERATION OF THE
PA2OOs
IC
(DRIVE
CONTROL)
.
Stroboscope Pulse
Circuit
1.
The platter
has
only
a
single
row of
stroboscopic
markings. Switchover
for
45 and 33 rpm
is
ef-
fected
by
changing
the frequency
of
the
pulse
to the
stroboscopic lamp.
2.
From the
Frequency Divider Selector
I,
a
fre-
quency
of
either
7\Hz (for
45 rpm, representing
1/80
of
6000H2)
or
55.5H2
(for
33 rpm,
repre-
senting
1/108) is obtained and
supplied
to
the
transistor that drives the stroboscopic lamp.
o
Reverse
Rotation
Prevention
1.
This motor
operates
indiscriminately
in
regard
to
the
direction
of
rotation.
If
the platter
is
turned slowly in the
reverse
direction by hand,
a
forward torque
will
be applied
until the platter
stops,
reverses
its
rotation and
reaches rated
speed
in the proper direction.
2.
If,
however,
the rotational
speed
in
the
reverse
direction
is
in
excess
of
33 or 45
rpm,
the
Forward/Reverse Command
Block may
"mis-
read" this
as
simply
excessive speed
("overrun")
and apply a
reverse
torque
until
rated speed
is
attained.
3.
This
reverse
torque
will
further
accelerate the
turntable rotation
in
the
reverse
direction.
This
is.known
as
"reverse run-away."
4.
To
prevent
this from
happening,
a
Reverse
Rotation
Prevention
circuit
has been
included.
5.
This
Reverse
Rotation Prevention circuit
con-
sists
of two flip-flops
and
AND
gates
See
Fig. 7-4.
6.
The
input
for
this circuit is
derived
from
the
Hall element position detection
signals processed
in the
Reverse
Rotation
Prevention circuit.
7.
As long
as
the platter is rotating in the
proper
direction, this pulse enters in the order
B -
A
-
C,
and
no "reverse"
command is generated.
8.
If,
however, the
platter rotates
in
the
reverse
direction, the pulse order
becomes
A
-
B
-
C,
and a corrective command is given to the
For-
ward/Reverse Command Circuit.
FFr
AND
FFz
S
a
n
R
SO
R
L--)
t r-
Forced Forward
Rotation
at 0 ou
Truth
table
o
Comparator Control and Forward/Reverse
Com-
mand
Circuit
1.
Two inputs
are supplied
to
the Control
Com-
parator: a)
a
4V
reference voltage from the volt-
age
stabilizer; and b) the output from
the active
filters, which
serves
as
the detection
signal.
2.
If
the turntable
rotates faster than rated
speed,
the
detection signal
is
higher than
the
4V
reference.
3.
When
this
happens,
the
Comparator Control
sends
a command
to
the Forward/Reverse
Com-
mand Circuit, telling
it
to apply
a reverse
torque
to the motor to
slow
it
down.
4.
Conversely,
if
^turntable
rotation
is below rated
speed, the detection
signal voltage
will
be
below
the 4V reference.
5.
In
this
case,
the
Comparator
Control
indicates
to
the
Forward/Reverse Command Circuit that
forward torque must be
applied
to the motor to
aicelerate it.
Operating
point
at zero
load
+
lnput
voltage
differential
between
0
pin
pin
A
V18...Voltageat
V19...Voltageat
pins (18) and (19)
Fis.7-5
(18)
(19)
Output
rtput
Fig.
7
-4
F
F-r
(
AN I)
FF:
S
Ti
()
at
l
)rrt 2oul (J
F]
o
1
o
1
o
o
o
A
1
o
1
o
o o o
I
cl o o
I
o
1 1
o
1
A
I
o
1
o
o o
o
.I
u
o
I
o
I
o o o
.I
C
o o o
I I
o
1
o
Area
of
5
17