Tektronix 1730 Series, Instruction Manual

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1730–Series Theory of Operation
4–3
X5 Gain is selected at the front panel. The limiter stage that follows prevents
overdriving of the Output Amplifier.
The conditioned video signal and the Y component of the Readout (from the
Microcontroller) are input to the Vertical Output Amplifier to match impedances
and normalize gain (approximately 40 V for 8 cm of vertical deflection) in order
to voltage drive the CRT vertical deflection plates.
Horizontal — Composite video from either internal (Channel A or B) or
external reference has all active video stripped away by the Sync Stripper to
leave only sync to output a sweep trigger. Remote sync, which bypasses the
Sync Stripper, triggers the sweep directly when enabled. Remote sync, which is
input through the REMOTE connector, requires an external enable.
A jumper determines the polarity of the remote sync for internal triggering:
Negative provides line rate triggering off a negative edge and field rate triggering
off a positive edge. Positive provides line rate triggering off a positive edge and
field rate triggering off a negative edge.
90 Hz (100 Hz for 1731) triggering, for D2-type video recorders, is also input
through the REMOTE connector. The 90 Hz triggering uses the Remote Sync
Input, with the internal polarity jumper set to negative sync polarity, and the
enabling jumper in the enabled position.
The output of the Sync Stripper (or remote sync) drives the Back Porch
Generator, Vertical Sync Recognition, and Horizontal AFC. Outputs from the
Vertical Sync Recognition and Horizontal AFC are used by the Field ID and
Trigger Select to trigger the Sweep Generator. If Calibrator is selected, the Cal
Drive signal from the Microcontroller provides the triggering signal.
The Horizontal AFC output, in conjunction with the Microcontroller, drives Line
Select, which outputs a pulse that:
1. Drives the Z-Axis Control to unblank the CRT at selected line(s).
2. Provides a bright-up strobe at the selected line(s) for 2 Field
Sweep.
3. Provides the Picture Monitor Output bright-up strobe.
4. Generates the Auxiliary Blanking strobe that is used by a
companion 1720-Series for line select.
The ramp signal, output by the Sweep Generator, drives the Mag Amplifier,
which provides three gain ranges, X1 (un-magnified Sweep), X10 (1
m
s/div. in
2 Line Sweep), and X25 (to display the full vertical interval in 2 Field Sweep,
while providing 0.2
m
s/div. sweep rate in 1 Line Sweep). The Horizontal
Positioning offset voltage is input to the Magnifier Amplifier to ensure sufficient
range to position any part of the display onto the graticule.