124
In the
MAX
position
of R16,
switch
S6 is
closed and
therefore
transistor
V2237
is
conductive.
Transistor
V2216
is also
conductive
and
short-circuits
C2217
so
that the timer
is
switched
off.
Erasure
can
now
only
take place
if
the ERASE
button
is operated.
STAB!
USA
TION
PULSE
GENERA
TOR
The
generator
itself
consists
of the
transistors
V2243
and
V2244,
which
function
together
as an
unijunction
transistor.
If
the
Q output
(pin
1)
of
D flip-flop
D2216
becomes
high, timing
capacitor
C2228
can
charge via
R2246
and R2251.
The
charging
of
C2228
continues
until
a certain
voltage
is reached
and
V2243
and V2244
fire
(become
conductive).
A discharge
path
is thus
provided
for
C2228 and
a low
pulse
is
available
at the
base
of V2243
and
the
collector
of
V2244.
The
oscillator
produces
pulses
with
a
frequency
of
about
150 Hz
and
a duty
cycle of
about
0,07 %.
The
D
flip-flop
D2216
switches
the
oscillator
on
the FAST
mode
900 ms
after releasing
the
ERASE
button
when a
positive
clockpulse
is
present
on
pin
3. The flip-flop
switches
the oscillator
off
when
a clear
pulse
reaches
pin 4
at the
start of
the
time-base.
When
the
instrument
is
switched
on,
a clear
pulse
of 550 ms
Is
applied
to pin 4
via
D2253.
This
pulse is
generated
by
the
circuit
comprising
inverter
02217/7,6
and timing
elements
R2314
and
C2231.
Pin
8 of AND
gate D2209
is low
in the
FAST
mode
from
900 ms
after
the release
of
the
ERASE
button
up
to the beginning
of the
time-base
sweep.
Pin
9 of AND
D2209
gate is low
in the FAST
mode from
1500ms after the
release
of the
ERASE
button
until
the end
of the
time-base
sweep.
As
a result,
pin 10 of D2209
is low from
900 ms after
the ERASE
button is
released
until
the
end of
the
time-base
sweep.
The
stabilisation
pulses are
available
on
pin 1
1 of D2231
from
900
ms
after t until
the
start
of
the
time-base.
During
the
time-base
sweep
pin
1 1 is high.
TIME-BASE
AND
Z-AMPLIFIER
CONTROL
The Z-amplifier
is
controlled by
the
storage logic
via
emitter-follower V2232,
R2278
and
V2267.
The time-base
is
controlled
via V2232
and R2287.
This circuit is
driven
on the
base
of V2232 by
a 100 ms timer
comprising
R2276, V2266,
D221
3/3,2
and
C2244.
The direction
of
diode V2266
is such that
this timer fuctions
differently
from
the other
timers: when
the input
becomes
high, the
output
is high
almost immediately.
When
the input becomes
low, the
output becomes
low
only after
a
delay
time
of
1
00
ms.
The input
signal for this
times
comes from the
discrete NAND
gate comprising
R2274
and
the
diodes
V2261,
V2262
and V2263.
The following
situations
are possible.
WRITE
mode: The
cathodes
of V2262
and V2263 are constantly
high. Pin
8
of
D2214 is also
high.
Pin
9
of
this NAND
gate is
low for 1200 ms
after the
moment that the ERASE
button is released.
Therefore,
output
pin
10 is high
during
the same time. Thus,
because of
the
100
ms delay time,
output
pin 2 of D2213 is high
for 1300
ms after
the release
of the ERASE
pushbutton.
FAST mode; The
cathode of V2261
and V2262 are
constantly high. Pin
5 of D2203 is also high. Pin
6 of
this NAND
gate is high
from 1 500 ms
after t(j until the end of
the time-base.
Because of the 100 ms delay,
output pin 2
of D2213 is low from
1600
ms
after
tg until the end of the time-base
sweep.
STORE mode:
The
cathodes of V2261, V2262 and V2263 are constantly
high
and
thus
output pin 2 of
D2213
is
constantly
high. In
this
mode,
the electron beam in the
c.r.t. is blanked by the
storage logic.
NON-STORE
mode (MEMORY
OFF): The cathodes of V2261
and V2263
are constantly high. The cathode
of V2262 is
constantly
low and thus the output pin 2 of D2213
is constantly
low.
In
this mode, the electron
beam
in
the c.r.t.
is not blanked by the storage
logic.
MISCELLANEOUS
CIRCUIT ELEMENTS
In the FAST
mode, the data
input (pin9) of flip-flop D2229 is high.
At
the
end of the time-base sweep
a positive clock
pulse reaches pin
1
1
and the flip-flop
reverts
to the set
condition:
output
Q
(pin
13)
becomes high.
The 100 ms
delay unit comprising
R2302,
V2228,
D2228/9,
10,
D2228/14,15 and C2238
is then
activated. After 100
ms,
a positive output pulse from the timer
reaches the
clear input (pin
10)
of the flip-flop
and resets
it.
The 100
ms timer
functions
in the same
way as the 100
ms, 500
ms
and
300 ms timers
that are
already described.
In the FAST
mode, the
data input
(pin
5)
of D
flip-flop
D2229 is high.
The clock pulse
reaches
pin
3,
600 ms
after
the
release
of the
ERASE
pushbutton and
the flip-flop
comes in
the set condition.
Now
the
output
Q
(pin
1
)
becomes
high. The 600 ms
pulse is
derived via
inverter
D2226/9,10
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