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Model 1331A
A5Q43/
A5Q44. In write
and
store modes, A5Q42,
A5Q43, A5Q44, and A5CR42 are all turned off. The
The waveform at the
collector
of A5Q41 is
applied
to the
CRT
storage
mesh.
When the ERASE push-
button is pressed, + 158 volts is
applied
to the base of
A5Q42. A5Q42 and A5CR52 turn on, discharging
A5C37. This causes A5Q43, A5Q44, and A5CR42 to
turn on, clamping the diode juntion
(A5CR41,
A5CR42, and A5CR43) to
about
-14 volts. At this
time, A5CR43 is turned off because + 158 volts is
applied
to the storage mesh. When the ERASE push-
button is released, + 158V is removed from A5R138
allowing
A5Q42
and
A5CR52 to turn off. A5C37
begins
to
charge
toward the + 158 supply through
A5R141. The rising
voltage
is
coupled
to the )unction
of
A5CR43
and
A5R136 through the Darlington
emitter
follower,
A5Q43/
A5Q44
(A5CR42
and
A5CR43
are
biased on). Finally the charge
across
A5C37 rises to back bias A5Q43; the Darlington pair
and
A5CR42 turn
off,
clamping the voltage
at
the
diode junction at
about
+14 volts with the output
following
one junction drop lower. At the
end
of the
erase
timing period, the pulse generator is
enabled,
the
storage
gate
is
enabled and
the
erase
pulses
are
again applied
to the CRT storage
mesh.
4-93. Collimator
Driver. The
collimator driver
consists of common emitter amplifier A5Q51 and
emitter follower
A5Q50. The purpose
of
the
colli-
mator in the
CRT
is to
shape the
flood
electrons
so
that they
arrive at
the
storage
mesh in parallel
paths perpendicular to the
storage surface.
The first
function
of
the
collimator
driver is to permit
accurate
and stable application of
the precise collimator
volt-
age for
best collimation. During the
erase
function,
because
the collector
mesh is placed in the path of
the flood
electrons,
there will be
areas
on the .storage
surface
behind the
collector
mesh where complete
erasure
will not take place because the flood electrons
are
deflected by the collector mesh. The second func-
tion of the
collimator
driver is to cause undercolli-
mation during the
erase
function. This causes the flood
electrons
to
arrive
at the storage
surface
at an angle
where they can flood those areas on the storage sur-
face normally shaded by the collector mesh. When the
output from the
erase
switch
goes
HI, it causes the
output
of the
collimator
driver to rise from +65 volts
to
+93
volts during the
erase
timing period.
4-94. Flood Gun Switch.
The flood
gun switch
consists of common emitter amplifier
A5Q45,
am-
plifier
/
switch
A5Q46,
and emitter
follower A5Q47.
When
the
input to A5Q46 from
the
flood gun
gate
is HI
(A5Q36
turned
off),
the
entire circuit
functions
as an amplifier and applies
pulses to the flood
gun
accelerator.
When A5Q36 is turned
on,
the base
of A5Q46 is grounded.
This
grounds
the
output of
A5Q45
and
turns A5Q46
off.
The
output of
A5Q47
goes
HI
and
the flood
gun accelerator is
turned
on constantly.
4-95. Deflector
Switch.
The
deflector
switch,
consisting
of A5Q57, A5Q58, and
A5Q59,
is a circuit
designed to cause a
large
voltage change at
its
out-
put.
Normally,
A5Q57
is turned
on and A5Q58 and
A5Q59 are turned off.
The
voltage on
the
collector
of
A5Q59
is
the
normal
voltage from
its
connecting
point on the y-axis amplifier (schematic 4).
Any time
a
blanking command
is
applied
to the blanking
am-
plifier, the
command
is
also applied
to the deflector
switch.
A5Q57 turns
off and
A5Q58
and A5Q59
turn
on.
This
applies
-49
volts
to
one
side
of
the
y-axis
amplifier,
unbalancing it
and causing any electrons
from the write gun to be deflected away from the
target area of the CRT. This prevents stored images
from being degraded by
spurious emissions
from the
write
gun.
4-96.
Blanking Amplifier. The blanking
ampli-
fier
consists
of common emitter
amplifier
A5Q49.
Its only function
is
to
invert
the blanking command.
4-97.
Unused
Circuitry.
Main
Assembly
A5
(pulse
circuits)
is used in
other
Hewlett-Packard in-
struments.
There
are some circuits shown on sche-
matic
7
that have no function
in
Model 1331A. Relay
driver A5Q40
and
relay A5Kl are not used. A5Q38
a
nd
associated components
has no
effect on
Model
1331A
although
it functions
as
designed.
Its
purpose,
when
installed in
the instrument
for
which it
was
designed, is to
cause a
15 to
30
microsecond delay
between
the
LO output of
the write
gate and
the
application of
the LO to the
storage gate.
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