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Theory of Operation
3–28
1780R-Series Service Manual
Diagram 10 Ramp Generator
The Ramp Generators produce the line and field sweep ramps for the waveform
displays. The slope of the ramp, for 1- 2- or 3-line or field sweep, is controlled
by a Digital-to-Analog Converter (DAC). Initiation of retrace and sweep start is
controlled, through sweep gates, by the +Ref H sync (line rate sweep) and V
sync (field rate sweep). The H and V pulses are gated in by the Line and Field
Sweep Gates to ensure that retrace does not occur during the active part of 2- or
3-line or field sweeps. In addition, the Field Sweep Gate implements the field 1,
field 2 triggering in the 2-field sweep rate.
The ramps are attenuated for Parade display of RGB (3-step) and YRGB (4-step)
external staircase signals. Both the staircase signal (to the horizontal) and the
/RGB Enable signal are input to the 1780R-Series through the rear-panel
REMOTE connector.
Line Sweep Gate. In the line sweep modes the LINE control line is high, U880B
inverts it and inputs it to U775B (an OR gate). The other input to the gate is
from U780A, which is also low (except at sync and retrace time). With no high
during active line sweep time, U775B output is low, which turns off Q589 in the
Line Ramp Generator to start the sweep ramp.
Overview
Circuit Theory