No Luminance
(No "Y")
A complete loss of the brightness portion of the video signal. The only thing that is seen is pure chroma. Some technicians & customers may call this a negative picture.
The fact is its not a negative picture at all. It is the strong presence of reds and blues. Chroma is only R-y & B-y information. Without luminance there can only be red and blue. Without the luminance portion, the RGB Matrix circuit cannot create the  needed green.

The area that needs to be looked at is the comb filter, luminance delay line, or any "y" path not limited to and including the comb filter. This symptom frequently effects vertical and horizontal sync integrity too.

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Dennis Viereck