Theory of Operation
3-2 WFM90D and WFM91D Service Manual
Top Board
The Topboard contains the microprocessor circuitry, the rasterizerand graphics
generator,the subcarrier oscillator, and the timing generator.
Microprocessor. Themicroprocessor takes input from the front-panel keypad to
control the operationof the instrument through the serial bus, parallel bus, and
dedicatedcontrol lines.
Rasterizer and Graphics. The rasterizerand graphics block produces all internally
generatedvideo including waveforms, graticules, and menus. The rasterizer uses
the horizontaland vertical deflection signals to produce the waveforms. The
rasterizeruses the horizontal and vertical sync signals from the Bottom board to
lock to the incoming videosignal.
The rasterizerneeds a good analog timing voltage to run correctly. This timing
voltage is generatedby a circuit loop between the Top and Bottom boards.
Problems with this circuitcan be on either circuit board.
Bottom Board
The Bottom board contains the power supply circuitry,the horizontal and
verticaldeflection circuits, the NTSC or PAL decoder, the vectorscope and
burst-lock circuitry,the sync separator, and the audio amplifier for the headphone
output.
LCD Display and Backlight(Serial Numbers B020100 and Above)
The LCD Display module generatesthe display graphics using input signals
generatedon the Top and Bottom boards. The power for the LCD Display
module comes from the Bottom board. The display backlight is incorporatedinto
the LCD Display module. See Figure 3--1.
LCD Display and Backlight(Serial Numbers Below B020100)
The LCD Display module generatesthe display graphics using input signals
generatedon the Top and Bottom boards. The power for the LCD Display
module comes from the Bottom board, while the power for the backlightcomes
from the BacklightP owerSupply board. The display backlight mounts into the
side of the LCD Display module. See Figure 3--2.