Video Signal Processing - Philips 7629 Service Manual

Video Signal Processing

Introduction
The video signal-processing path consists of the following parts:
RF signal processing.
Video source selection.
Video demodulation.
Luminance / Chrominance signal processing.
RGB control.
RGB amplifier
The processing circuits listed above are all integrated in the UOC TV processor. The
surrounding components are for the adaptation of the selected application. The I
is for defining and controlling the signals.
RF signal processing
The incoming RF signal goes to the tuner (pos.1000), where the 45.75 MHz IF signal is
developed and amplified. The IF signals then exits the tuner from pin 11 to pass through
the SAW filters (pos. 1002). The shaped signal is then applied to the IF processor part
of the UOC (pos. 7200).
Tuner AGC (Automatic Gain Control) will reduce the tuner gain and thus the tuner
output voltage when receiving strong RF signals. Adjust the AGC takeover point via the
Service Alignment Mode (SAM). The tuner AGC starts working when the video-IF input
reaches a certain input level. Adjust this level via the I
goes to the tuner (pin 1) via the open collector output (pin22) of the UOC.
The IC also generates an Automatic Frequency Control (AFC) signal that goes to the
tuning system via the I C bus, to provide frequency correction when needed.
2
C bus. The tuner AGC signal
2
C bus
2