Tektronix WFM601, Руководство по обслуживанию

Страница: 76 / 304

Theory of Operation
WFM 601 - Service Manual
3–19
frequency response characteristics of the CRT are compensated for by a network
between the VOUT+ and VOUT– terminals of U55.
Q10 and Q16 are power transistors that drive the CRT deflection plates. A
sample of the horizontal output voltage is fed into the emitters of the transistors
to compensate for CRT orthogonality error. U57A and B are noninverting buffer
amplifiers driving U64B, which converts the differential signals to a single
ended voltage that is applied through R168, the Y Align adjustment.
Diagram 13 Horizontal
The sweep generators are nearly identical buffered integrators. They are started
by either the line or field sweep speed signal from a DAC shown on Diagram 17.
For purposes of simplicity we will discuss only the Field Sweep generator.
The FLD SWP SPD signal from the DAC is filtered by an input filter with a 0.1
second time constant, R83 and C55. U39A is a buffer to drive U62A, an
integrator. C101 is the integrator capacitance. When retrace occurs, U63B
closes and discharges C101. When the FLD SWP SPD goes high, and U63B is
open, the output of U62A ramps up and provides the vertical sweep to the
Vertical Input Switch (Picture mode) and the Horizontal Signal Multiplexer.
The Horizontal Signal input selection consists of dual in-line package (DIP)
switch segments (U59, U63, U70, and U94) and an 3-to-8 line decoder (U60).
The decoder is controlled by three synchronous outputs from the Line Rate
Controller (Diagram 15). It is permanently enabled (pins 4, 5, and 6) so that any
change in state of the control lines (pins 1, 2, and 3) will pull one of the six
outputs (Y0–Y6) low and close the appropriate DIP switch segment.
The Horizontal Amplifier, U56, contains two independent amplifiers. The
external gain-controlled Auxiliary Amplifier is used as a single ended luminance
amplifier. The output of the Luminance Filter Amplifier (Diagram 11) is input to
the + input of the Aux amplifier. Its gain is controlled by the PIX CONTRAST
level from a DAC shown on Diagram 17. The single ended output drives an
inverting operational amplifier, U47B. The minus input of U47B is a summing
junction for the PIX BK LVL (black level) and the luminance from U56. The
output of U47B is the picture monitor intensity signal to the Z-Axis control
circuit (Diagram 19).
The main Horizontal Amplifier, which has inputs for horizontal signals and the
readout signal, converts the single ended input from the Horizontal MUX to a
differential output. In addition, it amplifies the differential input of the readout
Vertical Deflection
Sweep Generators
Horizontal Signal MUX
Horizontal Amplifier