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SM00025 Service Manual
and X202 (pins 4 and 5 respectively) pass through to pins 2 and 3 and pins 63 and 64 of I200, where they are demodulated.
1.8
1.8.1
RGB PROCESSOR (TDA9330)
VERTICAL DEFLECTION AND GEOMETRY CONTROLS
The drive circuit for the vertical and E-W deflection circuits are generated by means of a vertical divider which gets its clock from the line oscillator. The divider is synchronised by the incoming vertical pulse generated by the input processor (50Hz models) or the feature box. The vertical drive is realised by means of a differential output current. The outputs (100Hz/progressive scan models) must be DC coupled to the vertical output stage. The vertical geometry can be adjusted by I2C control via the service menu. 1.8.2 HORIZONTAL SYNCHRONISATION AND DRIVE CIRCUIT The horizontal drive signal is obtained from an internal VCO which is running at a frequency of 13.75MHz. This oscillator is stabilised to this frequency by means of a resonant oscillator 12MHz. The internal VCO is synchronised to the incoming horizontal HD pulse by means of a PLL with an internal time constant. The horizontal drive signal generated by means of a second control loop which compares the phase of the reference signal from the internal VCO with the flyback pulse. The time constant loop is internal. The IC has a dynamic horizontal phase correction input which can be used to compensate phase shifts which are caused by beam current variations. Additional settings of the horizontal deflection which are realised via the second loop are the horizontal shift and the parallelogram correction. The horizontal drive signal is switched on and off via the so called soft-start/soft-stop procedure. This function is realised by means of a variation to the Ton of the horizontal drive pulse. For EHT generators without bleeder the IC can be set in a fixed beam current mode. In that case the picture tube capacitance is discharged with a current of about 1mA which is determined by the black current feedback loop. With the fixed beam current option activated it is still possible to have a black screen during switch-off. This can be realised by placing the vertical deflection in an overscan position.
An additional function of the IC is the low-power start-up feature. This mode is activated when a supply voltage of 5V is supplied to the start-up pin. The required current for this function is 3mA typical. In this condition the horizontal drive signal has the normal Toff and Ton grows gradually from zero to about 30% of the normal value. This results in a line frequency of about 50KHz or 25KHz. The output signal remains unchanged until the mains voltage is switched-on. Then the horizontal drive signal will gradually change to the normal frequency and duty cycle via the soft-start procedure. The IC has a general purpose bus controlled DAC output with a resolution of 6 bits and with an output voltage range between 0.2V to 4V. 1.8.3 INPUT SIGNALS
The RGB control circuit of the TDA9330 (IZ04) contains three sets of input signals. Y, U, V, input signals which are supplied by the input processor or feature box. The nominal input signals for u and V are 1.33 VPeak-to-Peak and 1.05VPeak-to-Peak respectively. These input signals are controlled by brightness, contrast and saturation. Two RGB sources are intended for use by the SCART, while the second is used for the OSD and Teletext. The required input signal has an amplitude of 0.7VPeak-to-Peak. The switching between the internal signal and the OSD signal can be realised via a fast blanking . this input is only controlled by brightness. Switching between various sources can be realised 2 via the I C bus and by fast insertion switches. The circuit contains switchable matrix circuits for the colour difference signal so that the colour reproduction can be adapted for PAL/SECAM and NTSC. 1.8.4 OUTPUT AMPLIFIER
The output signal has an amplitude of around 2V black-to-white at nominal settings. The required white point setting of the picture tube is implemented by 3 separate gain settings for the RGB channels. To obtain an accurate biasing of the tube, a continuous cathode calibration circuit is implemented by means of a two point black level stabilisation circuit. By inserting 2 test levels for each gun and comparing the resulting cathode currents with two different reference currents, the influence of the picture tube parameters like the spread in cut-off voltage can be eliminated. 6
