Tektronix 070-8462-03, Instruction Manual

Page: 90 / 271

Theory of Operation
1735 HD High Definition Waveform Monitor
4–11
Horizontal Deflection Amplifier. The horizontal deflection amplifier consists of
Q32, Q31, Q29, Q28, Q30, and Q27. It differentially drives the CRT horizontal
deflection plates. The base of Q29 is the summing junction input for the
horizontal deflection amplifier. Q29 and Q28 form a differential pair that
converts a single-ended input to paraphase output and drives the output
transistors (Q30 and Q27). Common-mode voltage is fed from each output into
the emitters of Q28 and Q29 through R208 and R213. Q31 and Q32 are current
sources for the output stages.
When readout is active, the microcontroller switches off the sweep generator, the
horizontal position, and the RGB input amplifier. Diode switch CR9 is turned on
to enable the horizontal readout signal (ROHORIZ).
Focus Amplifier.
The FOCUS control affects two different display modes; normal
mode and LINE SELECT mode. In the normal mode of operation, the focus
voltage will be selected by the control setting only (Q1). When a LINE SELECT
(LINSTEP) pulse occurs, U3A turns off and additional current flows through Q1.
The LINE SELECT FOCUS adjustment (R6) is adjusted for optimum focus
while operating in LINE SELECT mode at the normal display focus setting.
Graticule Illumination. U4A is a triangle generator whose output is compared to
the front-panel SCALE control output level by U4B (a comparator). Whenever
the output of U4A is higher than the level from the front-panel SCALE control,
Q4 is turned on, and current is drawn through DS100, DS200, and DS300 to
ground. The duty cycle of Q4 is determined by the front-panel SCALE control.
J1 is normally in the 1–2 position (lights enabled). In the 2–3 position, the
graticule scale illumination is disabled.
Control / Post Regulators
Diagram <7>