Philips PM 5508 Operating Manual page 46

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49
The receiver operates as asimple-PAL-receiver during the lower part of the pattern.
Due to the type of signal applied the delay-line is inoperative and the effect
of possible incorrectly adjusted chroma demodu'ators will not be neutralised.
The upper part of the pattern is used as a reference, because owing to the PAL
system, these colours will not change until very large phase errors occur in the
demodulators (these colours will in fact only show a slight desaturation). The
changing of the colour in the lower part of, for example, bar 2 (containing only (B-Y)
information) is caused by the fact that, due to an incorrect phase setting of the
(R-Y) demodulator, this modulator is 'opened' at the incorrect moments and there-
fore produces an undesired output signal during bar 2. This signal produces another
colour in conjunction with the (B-Y) output signal.