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Theory of Operation
1780R-Series Service Manual
3–31
Whenever either End of Sweep Detector goes high U790B outputs a correspond-
ing high (Trig En) to synchronize cursor display, calibrator display, and
differential gain and phase displays.
Retrace Switch Blanking. Sweep blanking occurs whenever the output of U775D
(an OR gate) goes high. In field rate sweep modes, blanking is directly related to
the sweep retrace start and end. The blanking pulse is generated by U780C
(FIELD high) and U790D output high (duration of ramp retrace).
Blanking for line rate sweeps is about 0.1 ms longer than ramp retrace time.
U789A is a retriggerable one-shot multivibrator that stretches the retrace pulse.
U789A is triggered by the output of U775B going high to start retrace.
U780D provides blanking during switching between inputs for parade displays.
If either input of U775C is high (line select on or RGB enabled) U880A inverts
it and un-ANDs U780D. When neither of these conditions occurs, the output of
U880A will be high and a high on the SWITCH BLNK line generates a blanking
pulse.