Barco GRAPHICS 1209S, Руководство по обслуживанию

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Date : 10/02/98 R762271
Electromagnetic Focus+Hor Shift R762271
16
Sub module R762271S
Technical description
Obviously, the clamper Q310 shorts to ground the parabolic waveform, during the first
half of the horizontal scan, and Q309 shorts the signal during the second half of scan.
The buffered signals are now adjusted in amplitude with IC311, IC312 and IC313 for the
three colours. The outputs are summed and sent to the power amplifiers on a suitable
level.
b) At vertical frequency :
The vertical sawtooth "VDL" is DC coupled to a buffer IC308 pin 3 and then applied to
:
- the multiplier IC302 to generate a vertical parabola.
The parabola is inverted with Q304, clamped, buffered, and feeds two buffers in
IC309.
- a level detector IC308 input, pin 5, to produce a top-bottom squarewave. The
output is buffered and feeds the clampers Q311 / Q312 with a correct DC level
for grounding the input at either the top or bottom half of the raster.
The two remaining potentiometers of IC311, IC312, IC313 are used to adjust the top /
bottom waveforms which are again summed and leave the subunit to be amplified by
the power amplifiers on the main board.
c) Static or average focus (centre focus).
Three voltages R STATIC , G STATIC and B STATIC , adjustable b / - 1.5
volts with potentiometers in IC303 are added to the feedback of the vertical focus power
amplifiers.
d) Power amplifiers :
1. CORNER - H .
The left / right adjusted waveforms, summed on the subunit IC309 output, are
now amplified to generate the required magnetic field for focusing of the beam
during the horizontal scan. Because of the high scanning range, a good slew rate
of these amplifiers is necessary. This is especially critical during the second
part of the horizontal scan. This can be realised by boosting up the supply
voltage during this time.
This boosting up of the +FOC voltage is got with the circuit around Q190 - 193.
The squarewave drives the push-pull stage Q190 / Q191, which on its turn drives
the MOSFETs Q192 - Q193 . The +FOC voltage is boosted up during the second
part of the horizontal scan and is now referred to as +V[DYN].
Three identical amplifier stages with feedback to the inverting input of the
OPAMPs in IC100, deliver the required current to the horizontal focus coils.
2. CORNER - V / STATIC.
Since the vertical scanning frequencies are much lower than the horizontal
frequencies, a TDA2030 may be used. For stability reasons, a similar feedback
voltage is applied on the inverting input, together with a DC-voltage (=static, for
the centre).