Philips LX9000R/22, Service Manual

Page: 148 / 251

Circuit-, IC descriptions and list of abbreviations EN 148 LX9000R 9.
Figure 9-8
9.7.2 Loop trough
For ’Loop Trough’ the input video signals (CVBS, YC, YUV, and
YUV-progressive) from the Digital board are passing three
video switches before going to the Analog board.
•
Item 7503 for CVBS and Y/C.
• Item 7502 for YUV-interlaced.
• Item 7501 for YUV-progressive.
9.7.3 EPG RGB Video
A V-sync and H-sync (for progressive = 2H-sync) are
necessary for outputting an RGB video. A sync separator (item
7703) generates these syncs. Input for the sync separator is
either the 1fh or the 2fh luminance signal from the Digital board.
A video switch (item 7700) makes the selection. For
progressive video, the signal must be attenuated (item 7701).
The RGB signal goes via emitter followers (items 7202, 7203,
and 7204) to an RGB-to-YUV converter and to an RGB-to-
CVBS, Y/C converter.
The RGB-to-YUV converter consists of four OpAmp's, which
are necessary for RGB/YUV conversion (item 7600-B, -C, and
-D) and for adding the C-sync to the Y signal (item 7600-A).
The RGB-to-CVBS, Y/C conversion is realized by IC7602. The
oscillator (item 7601) is necessary for generating the chroma
carrier.
With transistor 7603 the conversion stages can be switched
'off' for power saving.
For the PIP (Picture in Picture) feature, the D_CVBS video
signal from the Digital board is used. This signal is fed to Pin 10
of IC7201. For scanning the EPG data, the A_YCVBS signal
from the Analogue board is fed to pin 8 of IC7201.
9.7.4 Power supply
The supply for the video stages and the EPG digital part, are
generated via DC-DC converters (items 7400, 7401, and 7403)
out of the 12STBY.