Tektronix WFM601, Service Manual

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Theory of Operation
3–4
WFM 601 - Service Manual
The Horizontal Amplifier is a variable gain amplifier with controlling inputs
from either the Microprocessor or the Line Rate Controller. Stage gain is
controlled by the Microprocessor-generated control voltages. Magnification is
switched by a signal from the Line Rate Controller.
An offset voltage horizontally positions the display. The amount of positioning
offset required for the Waveform mode is significantly greater than that required
for the other display modes; therefore, a separate offset is required. When CRT
readout is being processed the gain of the amplifier is changed by the Readout
Select signal from the Line Rate Controller.
The differential output of the Horizontal Amplifier drives the horizontal output
amplifier to normalize signal amplitude and drive the CRT deflection plates.
An additional amplifier stage within the Horizontal Amplifier provides a
differential output that controls the intensity for the Picture Monitor mode.
Picture Monitor contrast is controlled by the Microprocessor.
The Blanking Logic is a multiplexer that is controlled by the Line Rate
Controller. It selects the blanking/unblanking signals that drive the Z–Axis
Amplifier, which drives the CRT control grid.
Block Diagram 2
Component
The Y, P
B
, P
R
Reconstruction Filter outputs drive the Component/Blanking
Switching matrix. Switch output is buffered and becomes the input to the Color
Difference to GBR Transcoder, Bypass Switching, and Component display mode
switching.
The three channel outputs drive both the Component Display Switching matrix
and the Color Difference to GBR Transcoder. Either the color difference input
signal or the transcoded GBR signal can be buffered to drive the backporch
clamped Picture Monitor Output Amplifiers.
The Gamut Limit Detection circuit provides a flashing display on the Monitor
output when GBR gamut limits are exceeded. The Monitor Out display can be
either transcoded (GBR) or unprocessed components (Y/P
B
/P
R
). The Monitor
Out signals are clamped by a pulse that is generated by the Coprocessor (always
timed with the serial video). Composite sync, generated by the Coprocessor, is
added to the G/Y channel of the Monitor Out. The Y/G, P
B
/B, and P
R
/R outputs
are compensated in 75
Horizontal Amplifier
Blanking Logic
Component Blanking
Switching
Color Difference to GBR
Transcoder
Gamut Limit Comparator
and Clamped Amplifiers