Barco GRAPHICS 1209S, Service Manual

Page: 287 / 378

Date: 10/02/98 R762514
Dynamic Astigmatism module R762514
9
Technical description
TECHNICAL DESCRIPTION
" DYNAMIC ASTIGMATISM " 762514
The waveforms for the dynamic astigmatism are parbolic and resemble the waveforms
for the convergence corrections. It is then logic that the adjusted waveforms in the
Bella's are delivered by, and coming from, the convergence driver board.
These waveforms are carried to the module via the connectors J6 / J7 / J8. These
connectors carry the split (clamped) parabolic waveforms at horizontal and vertical
frequency and opposite polarity.
Each correction consists of an orthogonal spot correction (*X) and a diagonal spot
correction (*Y). To facilitate the correction a separate centre or 'screen axis' and corner
'screen corners' is provided.
In sheet 1 of the schematics you find the 12 Bella's for these corrections. As the
waveforms have opposite polarity, the supply voltages for these Bella's is +3.2V and
-1.8V taken from the convergence board.
The " corner" and "axis" corrections are added per colour and then passed onto the
power amplifiers. These power amplifiers are fully integrated hybrid amplifiers supplied
with + / - DYN.
The supply voltage for these amplifiers is +30V (+ DYN) and - 17V (- DYN) .
Each time the output current flows in 150 Ohm damping resistor across the stigmator
coils and a series feedback resistor of 4.7 Ohm. The voltage developed across this
resistor is sent back to the inverting input of the amplifier for stability reasons.
Note that the jumpers J3 and J4 can be removed in order to isolate the power stages
of the astigmatism and thus to investigate whether an excess of load on the supply
voltages of the whole convergence board is caused by one of these amplifiers (or
caused by another power amplifier of this convergence module).
diagonal spot correction
X-Y axial spot correction