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CUC 7305

Allgemeiner Teil / General Section

GRUNDIG Service

2 - 13

3.8 RGB Signal Path
For contrast control of the RGB signals, IC850-(23) generates a
variable control voltage for the contrast controlling amplifier at
IC150-(25). Because too high a beam current may cause damage to
the picture tube, the beam current is limited by this IC. The internal peak
beam current limiting function is carried out in the peak white limiting
stage. If the RGB signal exceeds 2.6V

, the internal peak white limiting

function starts working and reduces the contrast. The external peak
beam current limiting threshold is 2V

approximately.

The average beam current limiting function reduces the setting voltages
at IC150-(25) for the contrast.
After the brightness amplifier, the RGB signals leave the IC150 and are
passed on to the cathode amplifiers on the CRT base panel.

3.9 Generation of the Horizontal and Vertical Sync Signals
The TV signal processor IC150-(13,15) is connected to the CCVS
signal from the IF and from the EURO-AV socket. Following an internal
colour trap where the colour information is filtered off the CCVS signal,
the resulting Y-signal now divides into two paths. In one path the signal
is passed on for further processing, and in the other, the signal is
applied to the sync separator.
The sync separator produces the horizontal and the vertical synchro-
nising pulses from the Y-signal. The horizontal synchronising signal is
passed on to the

1 phase control, the vertical synchronising pulse is

used to start the line counter for vertical synchronisation.

3.10 Line Oscillator
With this IC concept, the line frequency is generated completely inside
the line oscillator. The IC is not connected to external components so
that it is not necessary to adjust the free running horizontal and the free
running vertical frequency.

3.11

1 Phase Control

The

1 phase control stage is for controlling the frequency. This stage

adjusts the frequency of the line oscillator to that of the line synchro-
nising pulse. For this, the frequency of the line synchronising pulse is
compared with the line oscillator frequency.
A

1 phase control stage defines the time constant of the control

voltage which is fed out at IC150-(40). The control voltage shifts the line
oscillator until the frequencies are equal.

3.12

2 Phase Control

The

2 phase control stage is for controlling the phase position of the

line drive pulse. This determines the phase off-set between the line
synchronising pulses and the actual position of the electron beam.
Dependent on the circuit components and the beam current, the delay
time between the external signal, the trigger signal and the actual
reaction of the line output stage is different. These differences are
compensated for by the

2 control.

To identify the position of the electron beam the line flyback pulse from
the line output transformer is applied to IC150-(38). From the oscillator
signal and the line flyback pulse the

2 controlling stage produces a

control voltage at IC150-(39) which is filtered by CC166.

Chroma-Signal

Farbkontrast vom

Prozessor

Colour Contrast

from Processor

Luminanzsignal

Luminance Signal

Burst

PLL

(R-Y)