Options—465B Service
Option 05
When
Q2854 is
cut
off,
C2856 discharges toward
ground
on a 30 microsecond time-constant,
starting at a
rate of about
—300
millivolts
per microsecond.
The
Q2854
emitter
voltage decreases
0 5 to
2.0
volts for the duration
of
a
2-
to 6-microsecond wide horizontal
sync or vertical
equalizing pulse For
the longer duration vertical
sync
pulses, the emitter voltage
decreases 4 volts (typical for
819/50 system with serrations)
to 5.5 volts (voltage
decrease stops when
the
emitter
reaches +4 2 volts since
the base is held
at
+4.7
volts).
When the collector of the
Q2834 Sync Amplifier steps
positive at
the end of the pulse,
a
negative-going
output
pulse is generated
at the collector
of
Q2854
that is
proportional
to
the amount
of emitter voltage decrease.
The
exact magnitude
of this
output pulse is a complex
function of
the rate of rise of the positive transition from
Q2834, the value
of C2856,
the
collector-to-base
capacitance of Q2854 (including
C2854) and the
collector-to-ground
capacitance of Q2854
The output
pulse at the Q2854
collector is approximately
80% of the
amount of
voltage decrease
The
positive-going trailing
edge of the differentiated
Q2854 collector
output pulse, which is coupled back
to the
base by C2854 and the 02854
collector capacitance,
creates
an overshoot at the base of Q2854.
This drives the
base
about
1
.5 volts above the
quiescent
level
at the end of
a vertical
sync pulse (this overshoot
does not appear on
the Q2834 collector
bus) The Q2854 collector waveform
stays negative
during the time the base
is
being
driven
positive; when the
base stops at the quiescent level,
the
collector voltage rises
rapidly, coupling an apparent
overshoot
into the base waveform This
condition tends to
delay
the start of the emitter voltage
decrease for vertical
serrations
following the first one,
but is otherwise
in-
significant.
The
output stage
bias network,
keeping
Q2863 cut off in
the
quiescent
state, inhibits the
output of
Q2854 collector
pubes
of
less
than
about 2 volts
peak (negative)
amplitude The larger
pulses
corresponding
to the trailing
edge of vertical
sync
pulses are large enough
to turn
on
02863. and provide
output signals of
1 to 2.5 volts at
the
input
end of
C2865. Because of the short rise
time of the
generated
pulses, the
output stage
responds
a small
amount,
even during
cutoff, due to
base-emitter
capacitance
in Q2863; this
is particularly
noticeable when
the load
is removed.
With
the load
disconnected,
the negative-going
output
pulses
are 2 to 2.5
volts in amplitude
(somewhat
smaller in
819/50 systems
with serrated
sync pulses),
with a rise time
of about 25
nanoseconds
and a width
of about 150
nanoseconds
Because they
are
so narrow, with
a low
repetition
rate, they
are hard
to
locate
in an oscilloscope
display. They are frequently misinterpreted as
to
their
presence or absence, their amplitude, and even polarity
(a
small trailing-edge overshoot
is
often
mistaken
for
the
pulse itself)
The output stage
is
diode-connected
to
limit
positive-
going peaks in the output. Output coupling capacitor
C2865 attenuates the signal, providing
a pro per
level
tothe
A Trigger circuits,
to permit correct A TRIGGER LEVEL
control action
ADJUSTMENT
PROCEDURE
Introduction
This procedure ensures proper
calibration and perfor-
mance of the TV
Sync Separator circuitry included
in
Option
05,
and
is based on the 525/60 line
and field
system If
your
Option
05 instrument is calibrated with the
equipment prescribed for
the
525/60
system, it should
perform satisfactorily
with other line and field
systems.
Before
starting
this procedure, make
sure
the
rest of
your instrument meets all
the specifications covered by
the Performance
Check or Adjustment Procedure
in the
main portion of this manual. For Option
05 instruments,
during the main Performance
Check or Adjustment
Procedure, use the
24
picofarad
Normalizer for vertical
attenuator input
compensation Refer
to Table
6-1
for
complete information
on the Normalizer.
Preliminary
Procedure for Sync
Separator
Calibration
1 Refer to the instructions
in the main portion of this
manual and remove
the front cover and cabinet from
your
Option 05 instrument.
2. Set the controls
as stated under Preliminary
Control
Settings for Option 05 calibration
3
Connect
the Option 05
1
nstrument
to
a power source
within the range
of its overall
voltage and
frequency
specifications.
4. Refer to
the
Performance
Temperature Spec-
ifications
in the Performance Check
or
Adjustment
Procedure
in the Specification section of this manual.
5. Allow
at
least
20 minutes warm-up before pro-
ceeding
6 12
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