Philips PM 5508 Operating Manual page 60

63
Fig. VII-38.
Incorrect
(G
-Y) signal
~ The level of bar 1 ((G-Y)) — 0) and bar 4 (grey) should both be zero
^
on the oscilloscope, see Fig. VII-37. If not, the signal from the
matrixing circuit is not correct. Because the (G-Y) signal is actually
matrixed from bhe (R-Y)- and (B-Y) signals, the fault will not
,,,,
necessarily be due to an incorrect matrix, but could also be
caused by, for example, an incorrect ratio of the output signals of
the delay line and/or the demodulator circuits. Fig. VII-38 shows an
incorrect (G-Y) output signal of the matrix.
^ ~
If the "zero"-level of green does not remain the same as for grey
when the contrast and saturation controls of the receiver are operated,
the chroma gain is too high (incorrect chroma AGC) so that the
(R-Y)
„_,
and/or (B-Y) signal is clipped, as a result of which their ratio changes
and the
(G-Y) signal also changes.
Note: The time base speed of the oscillograms is
approx. 6.5 his/division.