Philips PM 5508 Operating Manual page 36

39
Fig. VII-14. Vectorscope display of the "DELAY"-pattern
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1. ~ If the colour of bar 3 (from the left) differs considerably from bar 4,
first a coarse pre-adjustment of the subcarrier phase to the (B-Y)
demodulator should be made.
This is because the chroma signal in bar 3 represents (B-Y) = 0, and only contains
+ (R-Y) information. If the (B-Y) demodulator produces an output signal during that
bar, i.e. if that bar differs from bar 4 (the one without chrama), the subcarrier-phase
to the (B-Y) demodulator will not be correct.