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Theory of Operation
3–36
1780R-Series Service Manual
Sample-and-Holds. The sample-and-holds sample the output of the DAC when its
analog switch is closed. U708 is an analog multiplexer employed as a single-
pole, 8-throw switch. U245 is a dual-in-line switch package using three sections.
The Sampling Amplifiers are in U251, U605, and U810, which are Quad-Differ-
ential Amplifiers. The combination of the amplifier and its hold capacitor (C245
for WFM Horiz Position, U251B) hold the voltage while the DAC continues the
cycle of refreshing the rest of the sample-and-holds. Refresh occurs approximate-
ly every 10 milliseconds.