Tektronix 7834

Theory of Operation-7834
left vertical
unit to be displayed when the Vertical Mode
Command signal is LO and the signal from the right
vertical
unit to
be displayed when the Vertical Mode
Command sig-
nal is HI . When ADD vertical mode operation is
selected,
the Mainframe Mode Information signal is
HI . This allows
both the Right and Left Vertical signals to pass
to the out-
put . Now, the signal from both vertical units is
algebraically
added and the resultant signal determines the
vertical de-
flection . The X/Y Inhibit signal from the
Readout System
has absolute control over the output from this stage .
Quies-
cently,
this
signal is LO and the signal from the selected
vertical unit can
pass to the output . However, when the
Readout
System is ready to display information on
the crt,
this level goes HI, to block the signals from
both vertical
units .
HORIZONTAL
INTERFACE
The Horizontal Interface circuit determines
whether the
signal from the output of the A horizontal or
B horizontal
plug-in unit provides the horizontal deflection
signal . This
circuit also accepts an input from the Readout
System
(diagram 10),
which blocks the horizontal
signal while the
readout display is presented on the crt .
A schematic of the
Horizontal Interface circuit is
given on diagram 8 at the rear
of this manual
. Refer to diagram 8 during the following
discussion of
the Horizontal Interface circuit .
B Horizontal X-Y Delay Compensation
The Horizontal Interface circuit includes the
X-Y Compen-
sation network (Option 2 only)
.
This network
provides a
delay for the horizontal (X) signal from the
B HORIZ plug-
in compartment to match
the delay of the vertical (Y) signal
due to the delay line .
The horizontal (X) signal from the
A HORIZ plug-in compartment is
coupled directly to the
Horizontal Interface, without a delay
compensation
network .
TIME-BASE
OPERATION . When the plug-in unit installed
in the B HOR IZ
compartment is operated as a standard
time-base unit to produce a
horizontal sweep for deflection
of the crt beam,
the B Delay Compensation network is
effectively disabled .
The delay disable command, applied to
pin BY, is a
HI
and relays
K822-K838 are not actuated .
Therefore, the
relay contacts remain in the normally-closed
position so the
horizontal signal will pass directly through
this network to the
Horizontal Channel Switch .
X-Y OPERATION . If the time-base unit installed
in the
B HORIZ compartment is operated as an amplifier,
or if an
amplifier unit is installed in the B HORIZ
compartment,
the delay disable command to the B Delay
Compensation
network drops to the LO level
(zero volts) . This actuates
relays K822-K838 to
connect the B Delay Compensation
network
into the circuit . The B Delay (X-Y) Compensation
network is
an optional feature . For instruments which are
3-
34
not equipped with this feature,
the B horizontal signal
from
the B HORIZ plug-in
compartment is connected directly to
the Horizontal Channel Switch
(U884) through the Hori-
zontal Interconnect board
.
Horizontal Channel
Switch
The Horizontal
Channel Switch operates as a
switched
amplifier and
consists primarily of U884 . The
differential
horizontal signal
from the A HORIZ plug-in
compartment
is applied to pins
2 and 15 . The differential horizontal
sig-
nal from the B
HORIZ plug-in compartment is applied to
pins 7 and 10 . The
Display B control signal determines
whether the A or
B horizontal signal is coupled to
the out-
put pins 12 and
13 .
When the HORIZONTAL
MODE switch is set to
A the
Display B
signal, applied to pin 4 of U884, is LO
. This level
allows the
signal from the A horizontal unit to
pass to the
output
while the signal from the B horizontal
unit is block-
ed . In the
B position of the HORIZONTAL MODE
switch,
the level at
pin 4 of U884 is H I . Now, the signal
from the
B horizontal
unit is connected to the output
while the
signal
from the A horizontal unit is blocked
. When the
HORIZONTAL MODE switch is set
to ALT or CHOP, the
Display B signal at pin
4
of U884
switches between the HI
and LO levels, at a rate
determined by the Horizontal
Binary stage in the Logic
circuit . This action allows
the
signals from the
A horizontal unit to be displayed
when the
Display
B signal is LO and the signal from
the B horizontal
unit to be displayed when it is HI .
The
X/Y Inhibit signal from the
Readout System, diagram
10, applied to pin 6 of U884 has absolute
control over the
Horizontal Channel Switch stage .
Quiescently, this signal is
LO to
allow the signal from the selected
horizontal unit to
pass to the
output . However, when the
Readout System
displays
information on the crt, this signal
goes HI to block
the signals from both horizontal
compartments .
a-
Sawtooth
Out
OUTPUT SIGNALS
The Output Signals circuit
provides the +SAWTOOTH OUT
and -+ GATE OUT signal to
the rear panel . These output
signals are samples of signals
from the associated plug-in
units . A schematic of the Output
Signals circuit is given on
diagram 9 at the rear of this manual
. Refer to diagram 9
during the following
discussion .
The sawtooth
signals from the A and B time-base
units are
connected to the Sawtooth Amplifier stage
through series
resistors R192 and R193 respectively
(see Diagram 3) .
Sweep Selector S3320 determines
whether the A-sweep or
the B-sweep sawtooth
signal provides the
+
SAWTOOTH
OUT signal . The unused
sawtooth signal is terminated
by R3320 .