THOMSON VK231PS, Technical Manual

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87
LUMINANCE PROCESSING DURING RECORDING
In R6000 Series video recorders, luminance processing is performed by circuit IV001,
LA71500M.
Pin 28 of this circuit receives the composite video signal from Pin 3 of input selector IX001. At
the output of a clamp stage, the video signal is applied to Pin 35, at a stage of the AGC that
reacts only to the amplitude of the synchronisation time signals. This allows the video signal to
return to its original amplitude.
The video signal is sent to:
• Pin 38 of IV001 and impedance adapter TV020. This output is used for the control
channel.
• A 3-MHz cutoff frequency low-pass filter.
The purpose of this filter is to eliminate the chroma component of the composite signal, and
keep only the luminance component. The signal Y thus selected is applied to the vertical pre-
emphasis circuit, and is then available on Output 25 of IV001.
The signal is sent to the 3.9 MHz trap, which removes the remaining chroma component of the
luminance signal.
The signal returns on Pin 26 IV001 via Transistor TV005, and is sent to the detail enhancing
stages via a clamp stage.
A PAL/SECAM chroma detection circuit is used to issue the standard command from Output
62.