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Text excerpt from page 42 (click to view)
CP-520/520A/520F Service Manual WPR(GB) CL CCC-gain R(GB)-gain â0â â0â B6 B6 B5 B3 B5 B5 B4 B2 B4 B4 B3 B1 B3 B3 B2 B0 B2 B2 B1 â0â B1 B1 B0 â0â B0 B0 Max 64 Max 60 Max 126 Max 126
The setting of the gain registers of the 3 channels can be stored during switch off and can be loaded again during switch-on so that the drive conditions are maintained. When required the operation of the CCC system can be changed into a one-point black current system. The switching between the 2 possibilities is realised by means of the EGL bit (EGL = 0) in subaddress 42H. When used asone-point control loop the system will control the black level of the RGB output signals to the âlowâ reference current and not on the cut off point of the cathode. In this way spreads in the picture tube characteristics will not be taken into account. In this condition the settings of the âwhite point control registersâ(subaddress 20H-22H) and the âcathode drive level bitsâ (CL3 - CL0 in subaddress 42H) are added to the settings of the RGB preset gain registers (subaddress 23H - 25H). A black level off-set can be made with respect to the level which is generated by the black current stabilization system. In this way different colour temperatures can be obtainedforthebrightandthedarkpartofthepicture.The black level control is active on the Red and the Green output signal. It is also possible to control the black level of the Blue and the Green output signal (OFB bit = 1). In the Vg2 adjustment mode (AVG=1) the black current stabilization system checks the output level of the 3 channels and indicates whether the black level of the highest output is in a certain window(WBC-bit) or below or above this window (HBC-bit). This indication can be read from the status byte 01 and can be used for automatic adjustment of the Vg2 voltage during the production of the TV receiver. During this test the vertical scan remains active so that the indication of the 2 bits can be made visible on the TV screen. The control circuit contains a beam current limiting circuit and a peak white limiting circuit. The control is realised by means of a reduction of the contrast and brightness control settings. The way of control (first contrast and then brightness or contrast and brightness in parallel) can be chosen by means of the CBS bit (subaddress 44H). The peak white level is adjustable via the I2C-bus. To prevent that the peak white limiting circuit reacts on the high frequency content of the video signal a low-passfilter is inserted in front of the peak detector. The circuit also contains a softclipper which prevents that the high frequency peaks in the output signal become too high. The difference between the peak white limiting level and the soft clipping level is adjustable via the I2C-bus in a few steps. During switch-off of the TV receiver a fixed beam current is generated by the black current control circuit. This current ensures that the picture tube capacitance is discharged. During the switch-off period the vertical deflection can be placed in an overscan position so that the discharge is not visible on the screen. A wide blanking pulse can be activated in the RGB outputs by means of the HBL bit in subaddress 43H. The timing of this blanking can be adjusted by means of the bits WBF/R bits in subaddress 26H. DTV R&D Europe 41