Cameron KS21TK305A, Руководство по обслуживанию

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SERVICE MANUAL
36
ACL circuit is designed such that it only reduces the chroma signal and not the burst signal. This has
the advantage that the colour sensitivity is not affected by this function.
The SECAM decoder contains an auto-calibrating PLL demodulator which has two references,
viz: the divided reference frequency (obtained from the m-Controller) which is used to tune the PLL
to the desired free-running frequency and the bandgap reference to obtain the correct absolute value
of the output signal. The VCO of the PLL is calibrated during each vertical blanking period, when
the IC is in search or SECAM mode. The frequency offset of the B-Y demodulator can be reduced
by means of the SBO1/SBO0 bits in subaddress 3CH.
The base-band delay line is integrated. In devices without CVBS comb filter this delay line is
also active during NTSC to obtain a good suppression of cross colour effects. The demodulated
colour difference signals are internally supplied to the delay line. The baseband comb filter can be
switched off by means of the BPS bit (subaddress 3CH).
The subcarrier output is combined with a 3-level output switch (0 V, 2.1 V and 4.5 V). The
output level and the availability of the subcarrier signal is controlled by the CMB2-CMB0 bits.
1.8.11 RGB output circuit
In the RGB control circuit the signal is controlled on contrast, brightness and saturation. The IC
has a YUV interface so that additional picture improvement ICs can be applied. To compensate
signal delays in the external YUV path the clamp pulse in the control circuit can be shifted by means
of the CLD bit in subaddress 44H. When the YUV interface is not required some of the pins can be
used for the insertion of RGB/YPBPR signals or as additional CVBS(Y)/C input. When the YUV
interface is not used one of the pins (VOUT) is transferred to general purpose output switch (SWO1).
The IC has also a YUV interface to the digital die. Via this loop digital features like
“
double
window
”
are added.
A tint control is available for the base-band U/V signals. For this reason this tint control can be
activated for all colour standards. The signals for OSD and text are internally supplied to the control
circuit. The output signal has an amplitude of about 1.2 V black-to-white at nominal input signals
and nominal settings of the various controls.
To obtain an accurate biasing of the picture tube the
‘
Continuous Cathode Calibration
’
system
has been included in these ICs. The system is slightly adapted compared with the previous circuits.
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