Philips 7603 series, Руководство по обслуживанию

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These '' and 'V_DRIVE-' signals are applied to the input pins 1 and 2 of IC 7471 (full bridge vertical deflection
amplifier). These are voltage driven differential inputs. As the driver device (IC 7200) delivers output currents, R3474 and
R3475 convert them to voltage. The differential input voltage is compared with the voltage across measuring resistor R3471
that provides internal feedback information. The voltage across this measuring resistor is proportional to the output current,
which is available at pins 4 and 7 where they drive the vertical deflection coil (connector 0222) in phase opposition.
IC 7471 is supplied by +13 V. The vertical flyback voltage is determined by an external supply voltage at pin 6
(50V). This voltage is almost totally available as flyback voltage across the coil, this being possible due to the
absence of a coupling capacitor (which is not necessary, due to the 'bridge' configuration).
Deflection corrections
The linearity correction
A constant voltage on the horizontal deflection coil should result in a sawtooth current. This however is not the case as the
resistance of the coil is not negligible. In order to compensate for this resistance, a pre-magnetised coil L5457 is used.
R3485 and C2459 ensure that L5457 does not excite, because of its own parasite capacitance. This L5457 is called the
'linearity coil'.
The Mannheim effect
When clear white lines are displayed, the high-voltage circuit is heavily loaded. During the first half of the flyback, the high
voltage capacitors are considerable charged. At that point in time, the deflection coil excites through C2465. This current
peak, through the high-voltage capacitor, distorts the flyback pulse. This causes synchronisation errors, causing an
oscillation under the white line.
During t3 - t5, C2490//2458 is charged via R3459. At the moment of the flyback, C2490//2458 is subjected to the negative
voltage pulses of the parabola as a result of which D6465 and D6466 are conducting and C2490//2458 is switched in parallel
with C2456//2457. This is the moment the high-voltage diodes are conducting. Now extra energy is available for excitation
through C2465 and the line deflection.
As a consequence the flyback pulse is less distorted.
The S-Correction
Since the sides of the picture are further away from the point of deflection than from the centre, a linear sawtooth 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 those for the top and bottom lines. An S-shaped
current will have to be superimposed onto the sawtooth current. This correction is called finger-length correction or S-
correction.
C2456//2457 is relatively small, as a result of which the sawtooth current will generate a parabolic voltage with negative
voltage peaks. Left and right, the voltage across the deflection coil decreases, and the deflection will slow down; in the
center, the voltage increases and deflection is faster.
The larger the picture width, the higher the deflection current through C2456//2457. The current also results in a parabolic
voltage across C2484//2469, resulting in the fingerlength correction proportionally increasing with the picture width.
The east/west drive signal will ensure the largest picture width in the center of the frame. Here the largest correction is
applied.