30 Pg Coils A And B; 30 Pg Delay Multivibrator; Dc Holder And Amplifiers; Tracking Control Multivibrator - Sony AV-3600 Service Manual

with that in record
and absorbs control track
signal
deviations
caused by
wow
and
flutter.
30
PG
Coils
A
andB
Two PG
coils are
mounted on
the scanner (upper
drum)
180°
apart.
30
PG
coil
A
is
at
the
front of
the scanner
and 30
PG
coil
B
at
the
rear.
Both
PG
coils
are
connected between B
+
and ground through
R401 and
R402
respectively,
and
biased
at
about
2 V
dc.
Their
fields are cut
once per revolution
by
a
single
vane
(pole piece)
mounted on
the rotating
head platform.
Each 30 PG
coil
produces
a pulse
shown
in
Fig. 2-1.
Switching Pulse
Former and 30
PG
Pulse
Shaper-
FF401
Negative going
pulses of the
two 30
PG
coils are
coupled to bistable multivibrator
FF401
(hybrid IC)
through
D401
and D402.
A
pulse supplied to Pin
1 flips
FF401
and
a pulse supplied
to Pin 4
flips
it
back.
The
outputs
from
Pins 2 and
3,
identical
30-Hz
square
waves
opposite
in
phase, are applied to
switchers
Q205
and
Q206
through
integrators
R406/
C205 and R407/C206,
respectively.
A
sample of
the
output
from
Pin 2
is
supplied to
a differentiator
consisting
of
R408
and C404.
The
negative spike
from
the differentiator,
which
is
in
phase with
the
pulse
generated
by 30
PG
coil
B, triggers
MM401
to
supply the
gate
circuit.
30
PG
Delay Multivibrator-MM401
,
R412,
R413
Monostable multivibrator
MM401
(hybrid IC)
delays the
30
PG
pulse
(from 30
PG
coil
B) and
sets
the timing interval
between
the
vertical
sync
signal
(during record)
and
the
30
PG
pulse
from
coil
B.
Since the sync
signal serves as
the timing reference,
the time delay advances the angular position of the
rotating-head
platform with
respect to the video
signal.
MM401
produces
a positive pulse of
930
/xs
duration during record
and one
of
1.9
msec
dura-
tion during
playback
for
each
input pulse.
This
output pulse
is
differentiated
by C428
and
R448
and
the negative spike,
delayed
by
an
amount
equal to
the pulse
duration of
MM401,
is
supplied to the gate
circuit.
The
pulse duration,
i.e.
the delay time of
MM401,
is
selected
by SW7-8
according to the
mode
of
operation.
Thus,
the differentiated pulse
is
able
to
gate the integrated reference
30-Hz pulse
at the
proper position
on
the
ramp
to
produce
the
same
gating
output
in
record or playback
regardless
of the
dif-
ference in
30-Hz pulse waveshapes. See
Fig.
2-1.
R412
and
R413
adjust the pulse duration (delay
time) of
MM401
in
record and playback
operations
respectively.
Delayed 30
PG
Pulse Shaper
The
delayed
30
PG
negative pulse
is
amplified
and shaped
by Q404. Output
of
Q404
feeds the gate
circuit.
Dc
Holder
and
Amplifiers~C432
y
Q406, Q407,
R451,
R454
Gate output appears
across
C432, which
holds
the
level until
the following
gate output.
C432
sets
the gate-to-source
voltage of
Q406
and
thus
es-
tablishes
Q406
output. Direct coupled
dc amplifiers
Q406
and
Q407
supply
control current to the servo
brake
coil.
R45
1
sets the response time of the
servo
system
by
controlling
the
amount
of feedback
current
from
Q407
to
Q406 and
is
adjusted for
minimum
response time without
servo hunting.
A
large
amount
of feedback reduces the
ac gain of
the
amplifiers
and
prevents servo hunting but
it
increases
the response time.
R454
adjusts the
dc
gain of
Q406
to obtain
optimum
braking
current.
Control Track
Head-CTL
Head
During
record,
an output from monostable
multi-
vibrator
MM
404
is
applied
to the
Control-Track Head
(CTL
Head). This records
a
30-Hz timing reference
to
be used
during
playback
in
place of the
vertical
sync
pulse.
Control Track Pulse Amplifier-Q401
In playback, control track pulses
picked
up
by
the
CTL
head
are
amplified
by Q401
and
coupled to
Q402
through
a
noise
filter
consisting of
R418,C409,
andC410.
Tracking Control
Mutivibrator~MM40
3
When
the
TRACKING
control
(R007) on
tlie
Control Panel
is
pulled out during playback,
the
50-
Hz
pulse
from
MM402
is
coupled
to
MM404
via tlie
tracking multivibrator,
MM403
(hybrid
IC).
Mono-
stable multivibrator
MM403
compensates
for
O)
variations
in
control track information between
re-
corders, (b) tape
stretching,
and
(c)
tolerances in
physical
placement
of the
CTL
head. For
this pur-
pose,
MM403
delays the control
track pulse
arid
adjusts
the timing
interval
between
the video informa-
tion
and
the recorded
control track
pulse.
The
del^y
time can be
varied with the
TRACKING
control
R007, which
varies
the
pulse duration of
MM403.
2-4