Description des circuits / Circuit DescriptionCUC 7303 F
3.13 The Super Sand Castle - SSCOn reception of a synchronising signal, the line oscillator will first be
The 3-level SSC signal IC150-(38) is a composite pulse consisting ofsynchronised. In this case too, the line counter supplies a field deflec-
the line flyback, the field flyback, and the burst key pulses. The linetion signal. As soon as a field synchronising signal is obtained the saw-
flyback pulse (H-Sync) is fed through T523, CR163 to IC150. The fieldtooth generator will no longer be triggered by the line counter but
flyback and burst key pulses are generated inside the IC.directly by the field sync signal.
If the field deflection stage fails, IC400-(7) pulls the SSC level to "Low"The saw-tooth generator is made up of a constant current source which
via R401 and thus blanks the CRT at IC150-(18, 19, 20) RGB. In doingis used to charge and discharge an external capacitor. The charging
so, the analog values are set to "Low".period is determined by the field sync signal. The field deflection signal
can be measured at the capacitor C158, IC150-(43).
3.14 Setting of the Cut Off Voltage
Adjustment of the field amplitude at the field output stage IC400 is
An automatic cut-off controlling stage ensures that the static working
possible by influencing the field saw-tooth voltage. This alteration must
points of the CRT are held stable. For this, IC150 feeds out a pulse to
be carried out before the field output stage. For this, a feedback signal
the R, G, B cathodes during the lines 23, 24 and 25 to measure the
from IC400 is present at IC150-(42) for negative feedback. Similar to
beam current of each system (approx. 10?A). The cut-off current
an operational amplifier connected to the negative input, this technique
during the measuring lines is fed via the resistor CR156 to IC150-(14).
allows to set the desired parameters.
The IC compares this voltage with an internal reference value to
determine the working point for the black level of the video output3.17 Non-Interlace Compensation with Teletext (25Hz Modulation)
stages and the cut-off voltage of the CRT respectively.When a teletext (videotext) signal is displayed on the screen, the
teletext signal would continuously change by one line upwards and
3.15 The HDR Output Stage
downwards (non-interlaced teletext signal). To avoid the signal chang-
Following an amplification stage the horizontal drive signal for the line
ing the line, the teletext IC850-(52) supplies a 25Hz switching signal to
output transistor is provided at Pin 37.
IC150-(43). From this Uswitching voltage, a small DC voltage offset
25Hz
3.16 The Field Deflection Stageis derived for the deflection saw-tooth. This offset effects an upward
In this circuit concept, the field sync generator is substituted by a lineshift of the first half-field so that the even-numbered and odd-numbered
counter.lines are superimposed on each other.
When no synchronising signals are received the line oscillator is free
3.18 Coincidence
running. From this line oscillator the "vertical oscillator" is derived by
The coincidence information is generated in the IF stage and fed out on
counting the number of lines. After having counted 312 lines, the
IC150-(4).
counter feeds out a field sync signal so that the horizontal and also the
vertical deflection is achieved without using an external synchronising
signal.
Enable Oszillator
Enable OscillatorFlyback
Regelzeit-
Regelzeitkonstante
konstante für die
für die O 1-Regelung40363839
O 2-Regelung
Control Time Constant
Control Time Constant
for O 1-Control
for O 2-Control
37
ZeilenoszillatorO 1O 2HDR
Line Oscillator
H-Sync
FBASAmplitudensieb
CCVSSync Separator
V-Sync
Zeilenzähler44
+
Line Counter
VDR
-
4342
H/V-Synchronisation und Ablenkung
H/V Synchronisation and Deflection
SB25 HzVFB
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