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Theory
4-48. Some of the waveforms
indicated
on figure
4-5C are
present
only during prime
time
(time period
A). Others are present only
during
the erase timing
period
(time
period C). Still others are
present during
both prime time and the erase cycle. Prime time
plus the erase timing period is indicated
in
figure
4-5 as time
period
B.
4-49.
The
erase switch initiates 3 actions on 2
output
lines. Two
output
lines
are
required
because
different
circuits
require different
operating voltage
levels.
Both output
lines
go
HI during time period
C. One output
line
disables
the pulse
generator and
activates
the
blanking
gate.
The
other output
line
activates the collimator
driver.
4-50. Because
the flood
gun switch
is
activated (Al)
any
time Model 1331A is not in
store
mode, the pulse
generator
must be disabled during time period
C
to
prevent pulses from being
applied
through the flood
gun switch
to the flood
gun accelerator.
The HI
output from the
erase
switch
disables the pulse
generator.
4-51. One
input
to the blanking gate
was previously
activated
during
pulse
period A. The HI
from the
erase switch activates another
input during pulse
period C.
This
causes the output of
the
blanking gate
to be LO
during
both
periods
(pulse period
B).
4-52.
The HI
from the inverter
holds
the output of
the write gate LO;
now
both
inputs
to the storage
gate are LO so the output of the storage gate will
tend to go HI.
Its
rise to the
HI
state will be an
RC curve
because
the storage erase circuit is
robbing
current
from the
storage gate.
The
rising
voltage
at
the output
of
the storage erase circuit is
the result
of a charging capacitor.
As the
capacitor charges,
the
circuit
takes
less
current
until,
finally,
its
charge
path
is
cut off and the output of
the
storage gate
stabilizes
in its HI
state. At the end of
time period
C,
the
pulse
generator
is
enabled,
the storage erase
circuit
is
turned
off, and the erase pulses are again
coupled
to
the
CRT storage
mesh.
4-53. The output of
the
blanking gate
is LO during
time
period B.
This causes the
blanking
amplifier
to
apply
the blanking
signal (HI) to
the gate
amplifier.
It
a
lso
causes
the
deflector
switch to
apply
-49
volts
to
one
side
of the x-axis amplifier.
These
actions
assure
that no
electrons
from the write gun will
reach the target
area of
the
CRT
during the
erase
cycle.
4-54.
DETAILED CIRCUIT THEORY.
4-55. The following paragraphs
are
intended as
a guide
to understanding the functioning
of
the instru-
ment
and are
not
a
discussion of basic
electronics.
For instance, the text may
state
that
a circuit
func-
tions
as a
Darlington
amplifier and
assume that the
4-4
l\1odel 1331A
reader knows
how
a Darlington amplifier works. Un-
usual
circuits will be explained
in
greater
detail.
The detailed circuit theory
is keyed to
the sche-
matics
located in
Section
VIII. A reference is made
to
the
appropriate
schematic at the
pertinent
point
in
each
discussion. The
indicated
schematic
may
then
be folded out for reference while reading the text.
4-56.
LOW VOLTAGE POWER SUPPLIES.
4-57.
The low voltage power supplies
convert
line
voltages to
four
regulated
de voltages;
+50 volts,
-50volts,+12.6 volts, and+ 158
volts. The low voltage
power supplies consist of a
primary power
circuit,
a secondary
power
circuit, and a
regulator
circuit for
each
of
the de
outputs.
4-58.
Primary Power. See schematic
1.
Model
1331A can
be
operated from
either 115 vac, or 230
vac (single
phase,
48
to
440
hertz). LINE
ON
switch
Sl applies
power
to
the
primary windings
of
trans-
former
Tl. SELECTOR
switch
S2
connects
the two
primaries
in parallel
for
115 vac
operation or in
series
for
230
vac operation. Line
fuse Fl prevents
excessive
current from
damaging
the
instrument.
4-59.
Secondary
Power.
See schematic
1.
The
ac
voltage across each secondary
winding is full-wave
rectified
by
a
bridge
rectifier.
The
output of each
rectifier
is
filtered and applied
to
a
regulator. Trans-
former
Tl
also supplies 12 vac for
LINE indicator
DSl and 6.3 vac for the CRT
filament.
4-60.
-50
Volt Regulator. See schematic
1.
A
sample of
the
output
is
selected at
the rotor of AlR22.
Any
error
is
felt at the
base
of
A1Q5
and compared
with
a
reference
voltage
(developed by Al VR4) on
the
base
of
AlQ4. The difference is
amplified
and
applied to the
base
of
A1Q3.
Series
regulator
Q2
is
driven by A1Q3 in
such a
direction
as to correct
the error.
4-61.
+50
Volt Regulator.
See
schematic
1.
The
+50 volt
power
supply
is referenced to
a sample
of
the -50 volt
power supply
at
the base
of
A1Q2. A
sample
of
the output of
the
+50
volt supply is
com-
pared to the reference voltage. The difference is
amplified
by AlQ2
and applied
to the base of AlQl.
Series
regulator QI is driven by AlQl in such a
direction as to correct the error.
4-62.
+
158
Volt
Regulator.
See schematic 2. The
+
158 volt power supply is referenced to the -50
volt power supply
at
the base of A5Q2. Any
error
in
the +
158 volt power
supply
is
compared
to the
reference
voltage.
The difference is
amplified
by A5Q2
and applied
to the base of A5Ql. Series regulator Q3
is
driven by A5Ql in
such
a direction as to correct
the
error.
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