Technology of Q 2500 colour TV set

Technology of Q 2500 colour TV setAccording to the operating mode selection iseither with H level on blank on pins 38 and 33or controlled from the computer via the I²Cbus.In the following section of the circuit Y andcolour difference signals are generated fromthe RGB signals.4.7.2 Control stagesIn the Y path the first component is a circuitfor gamma correction and in the colour differencebranch the colour saturation settingstage.After RGB has been generated again from thedifference signals and the Y signal, the settingstages for contrast and brightness arereached.The control stages for contrast and coloursaturation in the other IC's are set to maximumand have no function. There is, in addition,in each channel, a setting stage for thewhite value, and the black value is set with theamplifier stages that follow.The white value and the basic setting of theblack value are determined in the two correspondingpositions of the service mode. Infurther a operation the black value is determinedby the cut off control.The RGB signals are output at a maximum of3.5 Vss via pins 40, 41 and 42.The measured values for cut off and leakagecurrent are fed to the IC on pin 44. With theevaluation circuits for leakage current and cutoff, together with the computer, subsequentadjustment is carried out via the output amplifier,in order to keep the picture impressionstable independently of aging.Pin 43 is connected to the base of the diodesplit transformer. The circuit integrated intothe IC thereby receives information about thebeam current flowing into the c.r.t.If the maximum permissible value is exceededthere, the circuit reduces the contrast and thebrightness with the corresponding controlstages. (see basic board “Beam current limitation“).4.7.3 I²C bus interface and raster correctionAll control processes such as brightness, contrast,etc are controlled via pins 10 and 11 ofthe I²C bus interface. In addition, a DAC canalso be controlled via the I²C bus. For this,TDA 9332 on pin 25 outputs an adjustablevoltage. This is fed to the rotation panel on pin3 of connector W 1021. At this point an additionalcoil on the tube turns the deflectionraster, thus providing compensation of theearth’s magnetic field at the installation site ofthe device. The value of the raster correctioncan set in both service mode and in the menufor picture functions.If the device is turned, the influence of theearth’s magnetic field changes. The plannedrotatable rack takes this into account. Therack is controlled from the chassis, with therotation angle being determined by the TVsoftware. Raster correction can also be determined,in that on rotation the voltage on pin26 of TDA 9332 is changed.The influence of the rotation angle on theraster displacement is almost linear. On installationof the device, it is sufficient for correctfunctioning of the correction to input a valuefor raster correction into the EAROM for thecentre and the two end stops.4.8 Picture in pictureOn the signal board an optional picture in picturecircuit is possible. This circuit consists ofthe video processorDocument Q 2500 105 © Loewe ProCollege