Technology of Q 2500 colour TV set

Technology of Q 2500 colour TV setW 511Pin 4Vertical output stageV-FlybackR559R563 C564U-SVMPicture formation is normally established bythe d.c. current component of the deflectioncurrent. This means that for a d.c. coupled Voutput stage, by simply changing the d.c.components of the control sawtooth, the d.c.component of the deflection current can bechanged, and with it the picture formation.C561D561UV+13VUV--13V246 3FlybackGeneratorSTV9379FAI 5612.6.1 Flyback generatorThe job of the flyback generator is to provide,the switching voltage for the voltage increaseduring the vertical flyback. The problem withthis is as follows:These two control signals contain all verticalcorrection information. This means that outputside S correction, which is necessary for a.c.coupled output stages, can be dispensed withcompletely. The component insert at the outputof the V output stage is also considerablyreduced. Symmetrical control almost fullysuppresses interference that can affect thetwo V control signals due to the very highcommon mode rejection ratio of the V-poweroperating amplifier. The two V control signalsV+/V- are applied to the pin connector W 511,pin 2/3 and reach the series resistors R 566/R 578 via the inputs on pin 1/7 of the V outputstage I 561. The sawtooth, which is amplifiedabout 10 times, is output by pin 5 of I 561 andforces the current through the vertical deflectioncoils.The R/C combination 568, from the output ofpin 5 to earth, prevents the tendency of theoutput stage to oscillate and protects it fromswitching peaks that can be caused by thedeflection coins. To stabilise the V outputstage, part of the sawtooth from the base ofthe deflection coils is fed back via resistorR 579 to the inverted input pin 1 .The energy requirement of the vertical outputstage is at its highest during the flyback, asthe electron stream has to be directed rapidlyfrom the lower right corner of the screen to thetop left corner.This transitory additional energy requirementis achieved by doubling the operating voltage,which is only available for the vertical outputstage. During the vertical trace, the bootstrapcapacitor C 563 is charged to approx. 26 V viaD 561. The output of the flyback generator atpin 3 of I 561 at this point is UV-/-13 V. At thetime of flyback start, the flyback generator isswitched by the output stage output at pin 5and applied to the output at pin 3 UV+/ +13 V.Due to the d.c. shift on the minus pin of capacitorC 563, the operating voltage for theoutput stage on pin 6 increases by the voltagein C 563. At the same time, D 561 is blocked,which prevents the charge in the power supplyleaking away. This means that for rapid flybackthere is a transitory +40 V (approx.) operatingvoltage available.For many c.r.t. types the flyback pulse is notsufficient to fully return the deflection beam,so that flyback lines are visible.Dokument Q 2500 29 © Loewe ProCollege