Tektronix 7B92A Maintenance Manual page 36

Slope Selector
above). Amplifier U322 selects the slope of the input
waveform on which triggering occurs. If pin 3 is high, the
time base will trigger on the negative slope. If pin 3 is
low, the time base will trigger on the positive slope. (The
internal signal is inverted by U274 before being applied
to U322.)
Slope Selector Amplifier (SN B069999-below).
Amplifier U284 selects the slope of the input waveform
on which triggering occurs. If pin 6 is high, the time base
will trigger on the negative slope. If pin 6 is low, the time
base will trigger on the positive slope.
signal is inverted by U264 before being applied to U284.)
The push-pull outputs (pins 7, 8 and 9, 10) of
U284 are connected to the inputs (pins 3 and 13) of
U304.
Output Amplifier
Amplifier U304 provides a final gain stage before driving
the trigger output tunnel diodes. The push-pull outputs
of U304 (pins 8 and 9) drive the emitter and base of
Q312. Transistor Q312 converts the push-pull output of
U304 to a single ended output to drive tunnel diode
CR314. As the emitter base voltage of Q312 increases,
the current through CR314 increases. When the current
through CR314 reaches 10 milliamperes, it switches to
its high level. The fast rise of CR314 is coupled through
C341 to the Arming Tunnel Diode, CR372, which also
switches high. The high level at the anode of CR372
increases the current through the Gate Tunnel Diode,
CR376. The rise of CR314 is also coupled through C324
(and a 1 nanosecond delay line) to CR376.
combination of the added current from CR372 and the
pulse from CR314 (1 nanosecond later) switches CR376
high. The fast-rise pulse from CR376 is connected to
the Delayed Sweep Generator.
Trigger Disable (SN B070000-above). At the
end of each Delaying Sweep, the Horizontal Logic
produces a Trigger Disable pulse to allow enough time
for the sweep generator to reset and stabilize before
another trigger pulse starts the next sweep. The Trigger
Disable pulse resets the main trigger output to a low
level. At the same time U820 pulls pin 3 AUTO high.
With pin CF low, and pin AH high (see Delaying Sweep
<> ),comparatorsQ402Q404, Q492-Q493 and Q482A-
Q482B reset to Q404, Q0492, and Q482B off and Q402,
Q493, and Q482A conducting.
differential comparators Q362, Q366 and Q342, Q346 to
Q362, Q342 off and Q366, Q346 on. With Q342 off, pin
2 of U322 is high resetting the Delayed Trigger.
Trigger Disable (SN B069999-below). At the
end of each Delaying Sweep, the Horizontal Logic
produces a Trigger Disable pulse to reset the Arming
and Gate Tunnel Diodes to a low level and allow enough
Amplifier (SN B070000-
(The internal
(SN B069999-below).
This resets the
time for the sweep generator to reset and stabilize before
another trigger Theory of Operation-7B92A pulse starts
the next sweep. The Trigger Disable signal is connected
to the base of Q332. When the Trigger Disable pulse is
high, 0348 and 0358 turn on, removing the bias current
from CR372 and CR376, respectively.
current, CR372 and CR376 both reset to a low level.
Delayed Triggering Modes (SN B070000-
above). The Delayed Trigger Generator operates in one
of three modes; Normal, Delayed (Runs After Delay
Time), and Delayed (Triggerable After Delay Time).
In the Normal mode (both Time/Division knobs
locked together), Q328 is cut off and U322 inputs are
disabled.
U322 gate goes high.
In the Delayed (Runs After Delay Time) mode,
the Delayed Trigger Generator operates the same as in
the Normal mode.
RUNS AFTER DELAY TIME switch, S250; but, there is a
delay between the time the Delaying Sweep Generator
starts and the Delay Pick off is generated. The Delay
Pick off pulse causes the gate of U322 to go high. In the
Delayed (Triggerable After Delay Time) mode, U322 is in
the Triggerable mode.
enables U322 to trigger when a trigger input signal is
present.
Delayed Triggering Modes (SN B069999-
below). The Delayed Trigger Generator operates in one
of three modes; Normal, Delayed (Runs After Delay
Time), and Delayed (Triggerable After Delay Time).
The In the Normal mode (both Time/Division knobs
locked together), Q334 is cut off and U284 and U304 are
both disabled. Additional current for CR372 and CR376
is supplied by R335 and R337. When the Delay Pick off
pulse cuts off CR381, CR372 switches high. The fast
rise of CR382 is coupled through R373 and C373 to
CR376, which also switches high.
In the Delayed (Runs After Delay Time) mode,
the Delayed Trigger Generator operates the same as in
the Normal mode.
RUNS AFTER DELAY TIME switch, S250, and there is a
delay between the time the Delaying Sweep Generator
starts and the Delay Pick off pulse cuts off CR381.
In the Delayed (Triggerable After Delay Time)
mode, the entire Delayed Trigger Generator is operating,
but the Arming Tunnel Diode, CR372, is held low by the
Delay Pick off signal until after the delay time.
When the Delay Pick off pulse cuts off CR381,
the next positive pulse from CR314 sets CR372 high and
1 nanosecond later sets CR376 high.
3-5
Theory of Operation-7B92A
When the Delay Pick off pulse goes high,
However, Q328 is cut off by the
Now the Delay Pick off pulse
However, Q334 is cut off by the
With no bias