Tektronix 1705A instruction manual Vertical Deflection Amplifier

Theory of Operation

Vertical Deflection Amplifier

control into the summing junction of U27 (pin 2). The Vertical Position control is attenuated by resistors R152 and R140 (2 dB POS RANGE). This positions the video signal at pin 6 of U27, providing greater positioning range while in High Gain mode.

The horizontal ramp signal from the Sweep Generator (Diagram 3) is approxi- mately 4 V in amplitude. Typical sweep length is 12 divisions. The variable resistor, R168, is one-half of the input resistance (Ri) for U26B, an inverting operational amplifier. The amplifier feedback resistance (Rf) consists of R180 and R177. Reducing the Rf of the operational amplifier while holding Ri constant reduces the gain, and in this case the sweep length. Strapping across W11 and W12 provides a convenient method of shortening the sweep to adjust the Horizontal Gain (R168) against the 10 divisions of the crt graticule. When the strap is removed the sweep length increases to 12 divisions.

Switches U30B and C are are enabled by the Readout Enable (/RO-EN) from the microprocessor (Diagram 5). When enabled, the input to the Deflection Amplifier is the X- (horizontal) and Y-Axis (vertical) components of the crt alphanumeric readout. The readout signal components are from the microproces- sor through a Digital-to-Analog Converter (DAC) (Diagram 5). The vertical positioning signal, from the front-panel VERTICAL POSITION control, is applied to the readout in order to common mode out positioning effect when the trace is repositioned.

The vertical output signal, or the Y-Axis readout, drives the base of Q26, one side of a differential input amplifier. The other side, Q28, is driven by the positioning voltage from the front-panel VERTICAL POSITION control. The signal from the collectors of Q26 and Q28 drive Q27 and Q29, common base amplifier stages. The gain of the Vertical Deflection Amplifier is approximately

7.The gain normalized output voltage, to drive the crt deflection plates, is developed across R229 and R230, the load resistors. Q22 and Q23 are a temperature-compensated current source from the -11.8 volt supply.

Horizontal Deflection Amplifier

Sweep ramp or X-Axis readout drives the base of Q17, one side of a differential input amplifier. The other side, Q16, is driven by the positioning voltage from the front-panel HORIZONTAL POSITION control (Diagram 5). The signal from the collectors of Q17 and Q16 drive Q14 and Q15, common base amplifier stages. The gain of the Horizontal Deflection Amplifier is approximately 20. The gain normalized output voltage, to drive the crt deflection plates, is developed across load resistors R178 and R179. Q18 and Q19 are a temperature- compensated current source from the -11.8 volt supply.

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