Grundig CUC 7303 Serviceanleitung Seite 32

Schaltungsbeschreibung / Circuit Description
3.13 The Super Sand Castle - SSC
The 3-level SSC signal IC150-(38) is a composite pulse consisting of
the line flyback, the field flyback, and the burst key pulses. The line
flyback pulse (H-Sync) is fed through T523, CR163 to IC150. The field
flyback and burst key pulses are generated inside the IC.
If the field deflection stage fails, IC400-(7) pulls the SSC level to "Low"
via R401 and thus blanks the CRT at IC150-(18, 19, 20) RGB. In doing
so, the analog values are set to "Low".
3.14 Setting of the Cut Off Voltage
An automatic cut-off controlling stage ensures that the static working
points of the CRT are held stable. For this, IC150 feeds out a pulse to
the R, G, B cathodes during the lines 23, 24 and 25 to measure the
beam current of each system (approx. 10µA). The cut-off current
during the measuring lines is fed via the resistor CR156 to IC150-(14).
The IC compares this voltage with an internal reference value to
determine the working point for the black level of the video output
stages and the cut-off voltage of the CRT respectively.
3.15 The HDR Output Stage
Following an amplification stage the horizontal drive signal for the line
output transistor is provided at Pin 37.
3.16 The Field Deflection Stage
In this circuit concept, the field sync generator is substituted by a line
counter.
When no synchronising signals are received the line oscillator is free
running. From this line oscillator the "vertical oscillator" is derived by
counting the number of lines. After having counted 312 lines, the
counter feeds out a field sync signal so that the horizontal and also the
vertical deflection is achieved without using an external synchronising
signal.
Regelzeitkonstante
ϕ
für die 1-Regelung
Control Time Constant
ϕ
for 1-Control
H-Sync
FBAS
Amplitudensieb
Sync Separator
CCVS
V-Sync
H/V-Synchronisation und Ablenkung
H/V Synchronisation and Deflection
2 - 12
Enable Oszillator
Enable Oscillator
40 36
ϕ
Zeilenoszillator
1
Line Oscillator
Zeilenzähler
Line Counter
SB
On reception of a synchronising signal, the line oscillator will first be
synchronised. In this case too, the line counter supplies a field deflec-
tion signal. As soon as a field synchronising signal is obtained the saw-
tooth generator will no longer be triggered by the line counter but
directly by the field sync signal.
The saw-tooth generator is made up of a constant current source which
is used to charge and discharge an external capacitor. The charging
period is determined by the field sync signal. The field deflection signal
can be measured at the capacitor C158, IC150-(43).
Adjustment of the field amplitude at the field output stage IC400 is
possible by influencing the field saw-tooth voltage. This alteration must
be carried out before the field output stage. For this, a feedback signal
from IC400 is present at IC150-(42) for negative feedback. Similar to
an operational amplifier connected to the negative input, this technique
allows to set the desired parameters.
3.17 Non-Interlace Compensation with Teletext (25Hz Modulation)
When a teletext (videotext) signal is displayed on the screen, the
teletext signal would continuously change by one line upwards and
downwards (non-interlaced teletext signal). To avoid the signal chang-
ing the line, the teletext IC850-(52) supplies a 25Hz switching signal to
IC150-(43). From this U switching voltage, a small DC voltage offset
25Hz
is derived for the deflection saw-tooth. This offset effects an upward
shift of the first half-field so that the even-numbered and odd-numbered
lines are superimposed on each other.
3.18 Coincidence
The coincidence information is generated in the IF stage and fed out on
IC150-(4).
Flyback
Regelzeit-
konstante für die
ϕ
38 39
2-Regelung
Control Time Constant
ϕ
for
ϕ
2
+
-
43 42
25 Hz VFB
CUC 7303
2-Control
37
HDR
44
VDR
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