Date : 10/02/98 R762519
Convergence module (OUTPUT)
9
R762519
Technical description " CONVERGENCE OUT" 762519
Technical description
The purpose of the power amplifiers is to bring the adjusted signals to a sufficient high
level that the convergence coils can be fully driven. Important hereby is that the drift
must be kept as low as possible and that the signals must be carried to the coils without
using coupling capacitors.
It is obvious that the coils react differently on signals at a high (line) frequency than on
low frequency signals. Much more power is required for the high scanning than for the
low scanning range. The power / - CONV for these power amplifiers is a variable
line frequency tracked voltage delivered by the "G2 + Diagnostic" board.
Six identical amplifiers feed the six convergence coils, two for each picture tube. We
'll discuss only the amplifier served with
"RHin" (Red Horizontal).
Note that "Horizontal " here relates to the moving direction (of lines of a crosshatch
pattern) and not to the "horizontal" frequency. The " RHin " signal contains waveforms
at line and vertical frequency.
That' s also the reason why the amplifier stages are identical.
The signal is first passed to the non-inverting input of an OPAMP MC34082, the
inverting input receives a feedback signal from the output. The purpose of this stage is
to stabilise the overall gain (DC and AC) of the amplifier.
The output of the OPAMP drives an inverting amplifier Q1 with high frequency
compensation in the emitter.
The input signal to the OPAMP is around zero level, Q1 is therefore supplied with +12V
and -CONV. The same applies for the next amplifier Q3.
This next MOSFET is supplied from the dCON
D
supply line through a variable
(line frequency tracked) current generator Q2, and, from the -CONV.
This dynamic voltage is the + / - CON voltage boosted up during the "pulse 2" time.
By this increased supply voltage the slew rate during the horizontal retrace time in
considerably improved. The end result is a better behaviour of the convergence coils just
after the retrace time, thus, in the beginning of the scan.
The dropped voltage across R12 / P1 / R13 is partially applied to the base-emitter
multiplier Q5 to provide sufficient voltage to drive Q4 / Q6 push-pull output stage.The
zeners just limit the gate - source voltage for protection.
The current flow from the + / - CONV is preferable symmetrical. If for some reason one
of the supplies is requiring more current than the other supply, the feedback system
can no more correct the situation. It is possible that the problem is caused by a lack
of symmetry of a pre- driver stage.
Further heating of an output that could lead to a breakdown might be avoided by
inhibiting the sawtooth generator (see schematic "Horizontal Axis Convergence",
sheet 1)
The electronic circuit that generates the
Ilim
is represented on sheet 2 of the "CONV
OUT" schematic.
The current taken from the + CON' develops a voltage across SR1 that is applied to the
base of Q20. The current taken from the - CON' does the same for Q21. As soon Q21
is switched on , the
Ilim
turns on Q22 (See sheet 1 of Horizontal Axis CONV) and the
sawtooth generator is inhibited.
Summary of Contents for GRAPHICS 1209S
Page 4: ...BARCO PROJECTION SYSTEMS GRAPHICS 1209S 90 00972 230V AC 90 00977 120V AC SAFETY NOTICE...
Page 9: ...BARCO PROJECTION SYSTEMS GRAPHICS 1209S 90 00972 230V AC 90 00977 120V AC GENERAL INFORMATION...
Page 28: ...BARCO PROJECTION SYSTEMS GRAPHICS 1209S 90 00972 230V AC 90 00977 120V AC SERVICE SHEETS...
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