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Akai VS-2EGN - Page 38

Akai VS-2EGN
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SERVO
12V
PB
Iv
fe)
TRACKING]
©
FROM
1¢1@0)
REFERENCE
SIGNAL
SERVO
12V
x
3
e
COMPARISON
SIGNAL
L}rraPezoio
SAMPLE
1
HOLD
1
ae
3
FF
3
|
GATE
y
TRAPEZOID
SAMPLE
+
GATE
2
HOLD
2
Bi
i
The
comparison
signal
having
entered
IC11
pin
(5)
is
amplified
by
the
PB
AMP,
and
fed
to
the
Mono-Multi
1.
Mono-Multi
1
is
triggered
at
the
leading
edge
of
the
com-
parison
signal.
The
delay
time
of
this
Mono-Multi
is
determined
by
the
time
constant
connected
to
pin
(4).
(@
During
recording
During
recording,
PB
12V
(‘L’)
is
inverted
at
IC9,
and
a
high
level
PB
signal
is
fed
to
IC10
pin
(6),
so
pins
(8)
and
@)
conduct.
As
a
result,
SERVO
12V
is
fed
to
IC11
pin
()
through
R79,
VR7,
and
R80,
which
deter-
mine
the
time
constant
of
the
Mono-Multi
along
with
C48.
@)
During
playback
PB.
12V
is
fed
to
IC10
pin
(5)
,
and
pin
(4)
and@)
con-
duct.
As
a
result,
SERVO
12V
is
fed
to
IC11
pin
(4,
through
VR9,
VR7,
and
R80,
which
determine
the
time
$----§-—--5---------
R92
Wy
R96
Wy
Fig.
7-35
shows
the
main
elements
of
the
capstan
motor
phase
control
circuit.
constant
of
the
Mono-Multi
along
with
C48.
Tracking
is
adjusted
by
varying
the
time
constant
of
the
Mono-Multi
by
the
Tracking
Control
Volume
VR9.
Discharge
current
of
C48
limits
the
internal
resistance
of
the
Mono-Multi,
and
delays
the
trailing
edge
of
the
control
terminal
pulse.
This
control
terminals
pulse
and
the
output
pulse
from
Mono-Multi
1
are
fed
to
the
next
Gate
1.
The
sampling
pulse
is
generated
by
means
of
the
delay
of
the
trailing
edge
of
the
CONTROL
ter-
minal
pulse
(pin
(14).
This
sampling
pulse
is
fed
to
TRAPEZOID
1
and
to
the
Sampling
&
Hold
(S
&
H)
Circuit.
A
reference
signal
(switching
pulse)
is
sup-
plied
from
IC1
pin
QQ
to
IC11
pin
(3).
TRAPE-
ZOID
1
is
triggered
at
the
traling
edge
of
this
refer-
ence
signal.
The
trapezoidal
wave
is
formed
at
the
TRAPEZOID
1.
The
leading
edge
of
the
trapezoidal
Service
Manual
VS-2EGN
wave
is
determined
by
C51
connected
to
pin
(e)
and
internal
resistance,
while
the
height
of
the
trapezoidal
wave
is
determined
by
R89
connected
to
pin
@.
The
trapezoidal
wave
and
the
sampling
pulse
are
fed
to
the
S
&
H
1
circuit.
The
phase
of
the
former
is
compared
with
that
of
the
latter,
and
C53
is
charged
with
that
pulse
voltage.
The
output
voltage
of
the
S
&
H
1
circuit
is
output
to
pin
(9).
Hunting
is
prevented
at
the
LPF
(R93,
R95,
C54)
,
and
the
output
voltage
is
limited
within
a
fixed
range
by
the
limiter
circuit
(TR6,
D12,
D13)
so
as
to
prevent
abnormal
rotation
of
the
motor.
The
output
voltage
thus
obtained
is
fed
to
pin
(3)
of
the
speed
control
servo
for
the
phase
control
of
the
capstan
motor.
35

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