Horizontal Output Amplifier (Diagram 6) - Tektronix 2246 1Y Service Manual

ramp at pin 9 crosses the second (delta) delay level
applied to pin 6. At that point, the DLY END 1 signal
is produced at the output of U315A (pin 2) and
applied to U602. A second B GATE signal is then
produced to start another B Sweep ramp to display
the signal at the delta delay setting.
Delay Time Switching
The DELTA DELAY and REF DELAY voltage level are
applied to multiplexer U301 from the DAC circuit.
The Measurement Processor
voltages based on the settings of the CURSOR/TIME
POSITION controls made by the user from the front
panel. Switch section U301A is held permanently
switched to direct the DELTA DELAY signal to its
output pin.
HORIZONTAL OUTPUT AMPLIFIER
(Diagram 6)
Horizontal Preamplifier
Horizontal Preamplifier 1C U802 converts single-
ended horizontal signals
horizontal readout, and X-Axis) into differential out­
puts to drive the crt horizontal deflection plates. The
horizontal preamplifier signals are selected by the
HDO and HD1 logic signals from Display Sequencer
U600 on Diagram 4. Magnified sweep, beam find,
horizontal positioning, and horizontal gain adjust­
ments (XI and X I 0) are provided in U802 and
associated components.
The function of each pin of U802 is as
follows:
RO (Pin 1): RO HORIZ. Input for horizontal
component of the readout display.
GA1 (Pin 2): Adjustment of R825 sets the
horizontal X I gain.
A RAMP (Pin 3): Input for the A Sweep
signal.
GND (Pin 4): Ground connection for U802.
B RAMP (Pin 5): Input for the B Sweep
signal.
MAG (Pin 6): Selects X I 0 magnified sweep
when high or normal sweep when low. Mag­
nified mode is selected when in X-Y hori­
zontal mode.
X (Pin 7): X-AXIS. This is the X-Axis signal
input when in X -Y horizontal mode. The
Theory of Operation—2246 1Y and 2246 Mod A Service
established those
(A sweep, B sweep,
signal source is the CH 1 trigger signal from
U421A (Diagram 3). Adjustment of R827
sets the gain of the X-Axis signal.
HDO (Pin 8): Pin 8 (HDO) and pin 11 (HD1)
are logic lines that select the horizontal input
signal to output differentially at pins 18 and
19. Table 3-24 gives the selection logic.
Table 3-24
HDO and HD1 Logic
HD1
HDO Horiz Signal Selected
0 0
0 1
1 0
1 1
V EE (Pin 9): -5 V supply to U802.
GA10 (Pin 10): Adjustment of R826 sets the
horizontal X I 0 gain.
HD1 (Pin 11): See the description for HDO
above.
ROUT (Pin 12): Horizontal Preamplifier dif­
ferential output signal for the right deflection
plate.
LOUT (Pin 13): Horizontal Preamplifier dif­
ferential output signal for the left deflection
plate.
BF (Pin 14): The BEAM FIND signal from
U503 (Diagram 4) switch the Beam Find
feature on or off. BEAM FIND on reduces the
horizontal deflection to within the graticule
area. Vertical deflection is also reduced and
the intensity is set to a fixed viewing level to
aid in locating off-screen, over-deflected,
or under-intensified displays.
POSITION (Pin 15): Input for the horizontal
position control signal. Multiplexer section
U301B switches to reduce the range of the
Horizontal POSITION control to match that of
the Vertical POSITION controls when in X-Y
horizontal mode. When X -Y display mode is
selected, a low XY signal on Pin 9 of U301B
connects the pin 5 input to the horizontal
position input of U802. The signal at pin 5 is
a reduced horizontal
produced by the R353/R358 voltage divider.
VCc (Pin 16): +7 V supply to U802.
RO HORIZ
A SWEEP
B SWEEP
X-AXIS
positioning signal
3-37