Specifications

Horizontal and trigger circuits

A block diagram for the horizontal and trigger circuitry is:

Figure 9

The horizontal and trigger circuits are responsible for the horizontal movement and positioning of the

electron beam. The trigger circuit causes the sweep generator to initiate a sweep of the voltage on the

horizontal plates in the CRT. This sweep is a sawtooth-shaped voltage that causes the electron beam

to sweep uniformly from the left edge to the right edge of the screen. This sawtooth is carefully

controlled for constant slope and period so that quantitative measurements of timing can be read from

the screen.

The trigger circuit is responsible for generating a sweep at the same point during the period of a

periodic signal. If this wasn't done, the screen would be a jumble of different waveforms, none of which

start at exactly the same place. The trigger level adjustment control on the front panel sets the voltage

on the input waveform at which the trigger event occurs -- and thus causes a single sweep of the

electron beam. The slope control allows you to select whether the trigger happens on the rising portion

of the signal (positive slope triggering) or the falling portion (negative slope triggering). Besides

triggering on the signal from the vertical amplifier, switches allow triggering from the AC line, an external

signal, or a TV signal.

The sawtooth waveform of the sweep circuit is as follows:

Figure 10

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