Tektronix 7834

A logic diagram of the Vertical Mode
Logic stage is shown
in Figure 3-21 . The discrete
components that make up each
logic function are identified .
Trace Separation
The Trace Separation stage is made up of
discrete compo-
nents 04438, 04442, 04448 and 04456
. This stage pro-
duces the Trace Separation output
to
the
Vertical Amplifier
circuit to offset the B-sweep display when
operated in a
dual-sweep mode (horizontal) . The level of this output
current is
determined by the setting of the VERT TRACE
SEPARATION (B)
control . The current from the VERT
TRACE
SEPARATION (B) control is switched so that the
Trace Separation
output is provided only when the B sweep
is being displayed in the ALT
or CHOP horizontal modes
and not when the B sweep only
is being displayed, nor for
independent-pairs operation (sweep slaving) .
Operation of
this stage is as follows :
The VERT TRACE
SEPARATION (B) control provides
current
to
the
Trace Separation output through R4456 and
04456
when 04456 is forward biased . When the B sweep is
being
displayed (for ALT or CHOP horizontal operation),
the Display
B signal at the base of 04442 is HI . This for-
ward biases 04442
causing its collector to go negative to
forward-bias 04448
. This causes 04448 to saturate and its
collector
goes positive to forward bias 04456 . During the
time
the A sweep is being displayed, the Display B signal is
LO . This
reverse biases 04442 and 04448 ; 04456 is reverse
biased, the VERT
TRACE SEPARATION (B) control is
disconnected
while the A sweep is being displayed .
When the HORIZONTAL MODE
switch is set to B (only),
a HI level is connected to the emitter
of 04442 through
R4431 . This reverse biases 04442 even
through Display B
at its base is HI for this mode . Therefore, the VERT" TRACE
SEPARATION (B) control has no effect . When the
VERTI-
CAL MODE switch is set to ALT and the
Delay Mode Con-
trol Out level from the A time-base unit
is LO (indicating
non-delayed
sweep operation), a HI level is applied to the
emitter of 04442 through
R4438 and CR4434 . This HI
level reverse biases 04442
even though the Display B level
is HI . This action disconnects
the VERT TRACE SEPARA-
TION (B) control for
independent-pairs operation so that
the vertical position of the B sweep display
is determined
by the slaved LEFT VERT plug-in unit only .
If delayed-
sweep operation is selected, the Delay Mode Control
level is
Theory of Operation-7834
HI to forward bias 04438 and 04443 . This allows the
VERT TRACE SEPARATION (B) control
to
position the
B sweep display, since independent-pairs
operation is not
possible when operating in a delayed-sweep mode .
A logic diagram of the Trace Separation stage
is
shown
in
Figure 3-22A . The discrete
components
which
make up
each logic function are identified
.
An
input/output table
for this stage is given in Figure 3-22B .
A TRIGGER SELECTOR
The A Trigger Selector circuit determines the source
of
the
internal triggering signals connected to the A HORIZ plug-
in compartment . Figure 3-23 shows a
detailed block
diagram
of the A Trigger Selector circuit . A schematic
of the
A
Trig-
ger Selector circuit is shown on diagram 5, at the rear of
this manual .
A
Trigger Channel Switch
The A Trigger
Channel Switch provides control signals for
the
Left
and
Right Trigger Preamplifier stages . 'The front-
panel
A TRIGGER SOURCE switch (S352) provides the
control signals
to operate the A Trigger Channel Switch .
When
the A TRIGGER SOURCE is set to LEFT, the A
Trigger
Channel Switch allows the Left Trigger Preamplifier
to
pass trigger signals from the LEFT - VERT plug-in com-
partment
to the A Trigger Output Amplifier . When the
A TRIGGER
SOURCE switch is set to RIGHT, the A Trig-
ger
Channel Switch allows the Right Trigger Preamplifier to
pass trigger signals from the RIGHT VERT plug-in compart-
ment
to the A Trigger Output Amplifier . When the A TRIG-
GER
SOURCE
switch is set to VERT MODE, the A Trigger
Channel
Switch allows the Left and Right Trigger Preampli-
fier stages
to pass trigger signals from the LEFT and RIGHT
VERT plug-in compartments
to the A Trigger output
Amplifier .
Table
3-2 shows the input and output conditions of the A
Trigger Channel
Switch, for each combination of the A
TRIGGER SOURCE
switch and VERTICAL MODE switch .
Notice that only the
A TRIGGER SOURCE switch controls
the output to
U520 and U580 when in the LEFT or RIGHT
VERT positions .
Also, Notice that the VERTICAL MODE
switch determines the output when the
A TRIGGER
SOURCE switch is in the VERT MODE
position .