Video Circuit Troubleshooting - Sony KDP-57XBR2 Training Manual

12. RA-4 Video Circuit Troubleshooting
Chapter 12 - RA-4 Video Circuit Troubleshooting
Overview
As mentioned earlier in this manual, the RA-4 chassis introduced Sony's first rear projection television with line
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doubling capability. New circuitry was designed to perform this task. The DRC , or digital reality creator, was
added to assist in doubling the horizontal scan lines by interpolating the video information for each of the 480
interlaced lines of the incoming NTSC signal. This would minimize the jagged edges that occur by simply
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doubling the lines. A more robust picture and picture circuit known as MID , or multi-image driver, was also
added to further enhance twin picture viewing and channel scanning. All of these new features required digitizing
of the video signal and that meant more components and a more complicated set of paths for the video to follow.
The upside of these add-on features is that they can be used to assist the technician in isolating the source of a
video failure.
Figure 12-1 will be the main diagram to be used for isolating video problems. It provides a great overall view of
the key video processing circuits and the different paths the various inputs and features will follow. The ability of
this chassis to accept component video allows the customer to take advantage of the higher chrominance resolution
capabilities of this format. It also provides a great troubleshooting path for bypassing most of the video circuitry.
Referring to Figure 12-1, it can be seen that A/V switch, IC515, controls all of the video selection except for
component sources that can be connected to the video 5 input. Any signal that is not a component format will
have the possibility of traveling either one of two paths: The main or the sub. All non-component video for main
viewing will route through the A/D converter, IC1309 (not shown on this diagram) and into the 3D comb filter,
IC1306. Even S video sources will be routed here. The 3D comb filter contains noise reduction circuitry for the
luminance signal and this will be done for S video sources. Composite signals will have chrominance separated
from the luminance. This is all performed in a digital format and then D/A converted within IC1306 to output
separated luminance and chrominance.
The Y/C signal now enters a decoder circuit. The 3.58MHZ carrier and sync will be removed so that only the R-
Y and B-Y chrominance levels are left. IC1307 is a switch that allows closed caption information to be inserted
and provides a direct path for a component video source directly to the DRC. The path will split at this point. One
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will go to the BM board that contains the MID to provide main video for the picture and picture feature. The
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other path will take the component signal to the BR board where the DRC will perform the line doubling. The
video information, now synchronized at 31.5KHZ, will enter the video processor IC511 where OSD can be inserted
and exit to the CRTs as RGB video.
The sub video path will be processed along a different path. A conventional comb filter is used and chrominance
will be decoded by IC1301. The sub component signal now enters a YUV switch, IC1302. This IC performs
several functions. It allows the insertion of closed caption information, main CPU OSD, and provides a point to
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route a component video source to the MID processor.
IC1004 supplies on screen graphics such as user menu and input/channel information. The BD board (auto
registration) supplies RGB information since it generates its own menu during convergence alignment along with
dot and crosshatch patterns.
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