Philips 27PS60S321 manual S-Correction, East/West correction

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During t3 - t5, C2490//2458 is chargedvia R3459. At the moment of the flyback, C2490//2458is subjected to the negative voltage pulses of the parabola as aresult of which D6465 and D6466 are conducting and C2490//2458is switched in parallel with C2456//2457. Thisis the moment the high-voltage diodes are conducting. Now extraenergy is available for excitation through C2465 and the line deflection. Asa consequence the flyback pulse is less distorted.

The S-Correction

Since the sides of the picture are furtheraway from the point of deflection than from the centre, a linearsawtooth current would result in a non-linear image being scanned(the center would be scanned slower than the sides). For the center-horizontal line,the difference in relation of the distances is larger then thosefor the top and bottom lines. An S-shaped current will have to besuperimposed onto the sawtooth current. This correction is calledfinger-length correction or S-correction.

C2456//2457 is relatively small, asa result of which the sawtooth current will generate a parabolicvoltage with negative voltage peaks. Left and right, the voltageacross the deflection coil decreases, and the deflection will slowdown; in the center, the voltage increases and deflection is faster.The larger the picture width, the higher the deflection current throughC2456//2457. The current also results in a parabolic voltageacross C2484//2469, resulting in the fingerlength correctionproportionally increasing with the picture width. The east/westdrive signal will ensure the largest picture width in the centerof the frame. Here the largest correction is applied.

East/West correction

In the T8, there are three types of CRTs, namelythe 100º, 110º and wide screen CRTs. The 100º CRTis raster-correction-free and does not need East/West correction.

The 110º 4:3 CRT comes with East/Westcorrection and East/West protection.

The wide screen TV sets have all the correction of the110 4:3 CRT and also have additional picture format like the 4:3format, 16:9, 14:9, 16:9 zoom, subtitle zoom and the Super-Wide pictureformat

A line, written at the upper- or lower side of the screen,will be larger at the screen center when a fixed deflection currentis used. Therefore the amplitude of the defelection current must beincreased when the spot approaches the center of the screen. Thisis called the East/West or pincushion correction.

The ‘Ewdrive’ signal from pin 15 ofIC 7200 takes care for the correct correction. It drives FET 7400.It also corrects breathing of the picture, due to beam current variations(the EHT varies dependent of the beam current). This correctionis derived from the ‘EHTinformation’ line.

7/8/2004