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2.@
Checking the demodulators.
Make sure that the chrominance-delay line is aligned before continuing the (R-Y) (B—Y)
demodulators.
The sub-carrier frequency should be applied to the (R—Y) and (B—Y) demodulator in a correct phase.
If not, in the third and fourth bar colour will appear (see Fig. 23). This is a result of a difference in
phase between the sub-carrier signal and the (R—Y) and (B—Y) signal.
When the demodulators are properly aligned, the third and fourth bar are grey. When the sub-carrier
phase difference between both modulators is not exactly 90°, it has to be adjusted.
This phase fault will then appear as a coloured third or fourth bar (depending on the type of receiver)
see Fig. 24. There are receivers with a 90° (R—Y) reference (third bar) or with a 90° (B—Y) reference
(fourth bar).
3.@
Checking the matrix.
When the blue- and red gun are switched-off, the first 2 bars have the same green intensity when
the G—Y matrix is properly aligned.
|. PATTERN 9
"Colour bar"
But above all this pattern is used to check for good overall-colour performance.
The colour-bar pattern can also be used for the following receiver- or V.C.R. checks and adjustments.
Receivers:
1.™@ > Checking the burst keying
2.™
Checking the colour AGC and the colour killer
3.8
Checking the reactance circuit of the subcarrier regenerator
4a
Checking the synchronisation of the subcarrier regenerator
5.8
Checking the PAL identification circuit
V.C.R.:
l.o
Check the saturation of the V.C.R.
'
The alignments of the writing currents for the video head are critical. The ratio between the colour
carrier, 562.5 kHz with 75 % saturation, and the black and white carrier measured on the video had
is 1:10. Under these circumstances and when the filters, which determine the transmission range
between luminance and chrominance, are adjusted properly there is no mutual influence.
3.0
This pattern can also be used to check whether there is a delay between the colour- and the blackand
white signal. As the two signals are processed separately, there must not be any delay between th:
luminance- and the colour signal.
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