Technology of Q 2500 colour TV set

Technology of Q 2500 colour TV setA free DAC in I 2271 is used for horizontaloffset correction. The d.c. voltage felt on pin55 can be set in the servicing mode. This isfed via connector W 511 /W 1511, pin 8, to thebase of transistor Q 533 on the basic board.Q 533 together with R 555 represents a currentsource for the push-pull stage Q 531 andQ 532. The operating point for the push-pullstage is set with R 537 and the parallel circuitof R 535/538/539. At rest the operating voltageof the line output stage is applied to thebase connections of Q 531/532 and both transistorsare blocked.If I 2271 increases the base voltage of transistorQ 533 and this then conducts, the basevoltage of the push-pull stage drops and Q531 conducts. This means the d.c. current ismade more negative by resistors R 516,R 517 and R 518 and coil L 530, whereby thedeflection shifts to the left.If, on the other hand, the voltage on pin 27 ofI 2271 drops, transistor Q 533 becomes highresistance and the base voltage on the pushpullstage increases. This means Q 532 conductsand L 530 increases the voltage on pin2 of the deflection coil. This leads to a shiftingof the d.c. current component in a positivedirection and deflection to the right. Coil L 533serves as d.c. current coupling for the deflection.2.5 East/west correctionIn order to compensate for the pincushion(distortion) in 110° units in an east/west direction,the horizontal deflection current in thevertical centre must be increased with respectto the vertical start and vertical end. The rightdegree of correction is achieved by influencingthe horizontal deflection current with a verticalfrequency parabola in the east/west diodemodulator.Two generators connected to each other by abridging circuit provide the correction signalfor the E/W modulator for the horizontal deflectioncurrent.G1G2C1C2L1L2UB2D1D2UB1In the above drawing the two generators, G1 =horizontal generator, and G2 = east/west generator,are represented only by their resonantcircuits. The deflection current in the deflectioncoil L1 is supplied by both generators. Sothat the high voltage is not influenced by theE/W modulator, the voltage on transformer THis determined only by the horizontal generatorG1. Therefore, for correct bridge compensationduring the line trace, only E/W modulationof the deflection current takes place in an almostnon-reactive fashion on the horizontaloutput level. For improved clarity the conceptualflow diagram above is shown in the followingdrawing with the actual componentlocations.STHDocument Q 2500 26 © Loewe ProCollege