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Flip-Flop
1C601(1/3)
Monostable
MV
Q603, Q604,
Q605 and
Q606
AND
gate
Q607
Integrator
R625, C620
31.25 kHz
X'tal OSC
Q65 1, Q652
£/2, & £/625
count down
1C651
Flip-flop
1C601(1/3)
8-4
The flip-flop is triggered by the
negative
slope of the
Schmidt
output
so
that
the
13,125 Hz
frequency is halved to 6562.5 Hz
rectangular pulses.
The positive slope of the mono-
stable multivibrator
is triggered
by the
negative
slope
of the
flip-flop
output.
The negative
slope
of
the
multivibrator
is
determined
by
potentiometer
R621
so that the ON period of
the multivibrator is always held
constant
by R621.
Since the
ON
period
of
the
flip-flop
varies with the head
rotational
speed
whereas
the
ON
period
of the multivibrator
is always
held
constant,
the
error
signal
is obtained
by comparing
the
flip-flop
output
and = multi-
vibrator output.
The
monostable
multivibrator
output (Fig. 8-3-4) and the flip-
flop output (Fig. 8-3-3) are fed
to
an
AND
gate,
Q44,
that
conducts
only when
the mono-
stable
multivibrator
and
the
flip-flop
are
ON
at the same
time.
The
duration
of
the
AND
gate output pulse depends
on the speed
of head rotation.
If head
rotation
is too
fast,
the flip-flop
output
pulse
will
have a short period as compared
with
the
constant
monostable
multivibrator output pulse. The
AND gate output will then have
a long pulse duration.
The
AND
gate output
is con-
verted
to
a
dec level
by
the
integrator circuit.
This
is a conventional
crystal
controlled oscillator operating as
a syne
generator
for camera.
An
IC
type
MN-116
receives
31.25 kHz
input
and
provides
f/2 (15,625 Hz)
and
£/625
(50 Hz) for camera drive.
Divides the 50 Hz VD pulse to
25 Hz rectangular pulse.
Integrator
R728, C723
Gate
Q707
Hold
Q708
Dc amp
Q709
The rectangular pulse is integrat-
ed
so
that
both
positive
and
negative edges have a slope deter-
mined by the RC time constant.
The integrator output is sampled
by the 25PG pulse to obtain the
servo error signal.
The sampled signal charges C725
until next sampled signal comes
in.
Q708
has
the
high
input
impedance so that C725
charge
will
not
be
discharged
during
gate is closed.
Error signal between the VD and
25PG is represented by dc signal
that is supplied to the reference
multivibrator
that
is
made
variable so that head disc scanner
and camera
deflection is locked
in.
8-2-2.
TV Record
Mode Servo
In the TV record mode the same
servo system
is used to drive the scanner except that the master
crystal oscillator signal is replaced by the separated
TV sync. The capstan servo is not operative in the TV
record mode.
Sync separator
Q704
Low-pass filter
C715, C716
Flip-flop
IC601(1/3)
Integrator
R728, C723
Gate
Q707
De amplifier
Q709
'
This
is
a
conventional
sync
separator
with
a
short
time
constant. bias network (R713 &
C712)
to
remove
impulse-type
noise.
Removes horizontal, sync pulses
from
the vertical
sync interval.
Divides the 50 Hz vertical sync
pulse
to
a
25 Hz
rectangular
pulse.
a
The
rectangular
pulse
is inte-
grated so that both positive and
negative.
edges
have
a slope
determined'
by
the
RC
time
constant;
ee
The
integrator output
is gated
by the 30PG
pulse to obtain
the servo error, signal.
The
error
signal
is amplified
by Q707, and fed to the mono-
stable multivibrator (Q603 .~
Q606) so that the error signal
can vary the time constant of the
monostable multivibrator.
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