Barco GRAPHICS 1209S, Руководство по обслуживанию

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Date : 10/02/98 R7621127
Sync+Vertical Deflection R7621127
18
Technical description
2. The amplitude of the input signals is limited to + 3.2V and -1.7V. Measures must
be taken to avoid saturation of the input.
The control of these IC’s is accomplished with a SCL (serial clock) and SDA (serial
Data) which come from the controller. The address of the IC is determined by the
address pins which are grounded or left open (=high).
Obviously, as one IC contains four potentiometers, the address of the IC is followed
by a “slave” address selecting the correct potentiometer "0", “1”, “2”, or "3".
d) Vertical linearity control
Vertical Linearity control is obtained by adding an adjustable vertical parabola to the
sawtooth waveform. That adjusted parabola is in fact the sum of a parabola with fixed
amplitude and a parabola with variable amplitude.
The sawtooth is buffered with OPAMP (12 - 13 - 14 of IC407). Behind the buffer we
have two outputs for further processing :
a) the V SWT , sent to the multiplier, to generate a vertical parabola, and for the
keystone correction (E/W correction).
b) the VERT SWT , sent to the Bella IC400, for the vertical amplitude control.
The V LIN PAR (pin 7 output of IC406) is applied to :
- the Bella IC400 to adjust the amplitude, the output is labelled " %V LIN PAR ."
- the OPAMP IC406 input pin 2 (to be added to the adjusted V LIN PAR ).
The OPAMP 1 - 2 - 3 adds the VLIN PAR to the %V LIN PAR and the output is added
to the V SWT by R409 / R410.
e) Generation of vertical pulses from the vertical sawtooth.
1. Pulse for overshoot in the deflection
The "black" cathode currents are measured during a small time at the end of the
vertical retrace time (top of the picture). To allow a correct measurement, the three
beams may not be blanked during that time.
This means that the spot can be visible at the top of the picture.
An extra movement of the electron beam in the vertical deflection at the moment of
unblanking can move the "visible beam" to a point beyond the screen. For this extra
excursion (or "overshoot" in the scanning) a pulse is generated as follows.
The "V SWT" is capacitively coupled to the trigger input (negative going transient) of
IC 414. R492 / R493 installs a DC offset at this input.
The pin 13 (positive polarity) output pulse drives the Mosfet Q402 into saturation at
the end of the vertical flyback to produce a maximum excursion of the spot.
The other opposite polarity output of this one-shot , "BL PULSE INV", is used for
blanking (see later).
Due to the integrating behaviour of the scan coils, the current is delayed with respect
to the voltage.
The ABL pulse to be used in the "RGB - DRIVER " module for the black current
measurement has to be delayed with respect to the above “overshoot-pulse”.