Video Process Troubleshooting; T & S Models - Sony KDP-57XBR2 Training Manual

6. RA-3/3A Video Process Troubleshooting: T & S Models
Chapter 6 - RA-3/3A Video Process Troubleshooting:
T & S Models
Overview
One of the more significant video features introduced in the RA-3 chassis was addition of component video input.
This was added to all models from the T series all the way up to the V line. Since DVD and satellite boxes were
offering this video format, it was a welcomed addition, which took advantage of its better picture quality capabilities.
The other new feature, only available on the V line models, was Twin View Picture and Picture. It allowed the
customer to watch simultaneous, live programming side-by-side. The video paths are slightly different between
the S and V lines so they will be covered separately.
What is the advantage of component video? "S" video eliminates chroma cross talk, so this issue is not relevant.
The luminance bandwidth of both composite and S video is the same as component, so what exactly is the
advantage? The most common answer would be "Less processing of the chroma". While this may be true, it has
nothing to do with the one, distinct, advantage. Composite and S video utilize the 3.58 MHZ carrier. Component
does not. Although broadcast NTSC is limited to 4.2 MHZ of luminance bandwidth (because of transmission
bandwidth), recording and playback devices are not. VCRs are the exception, however, and their bandwidth is
restricted even further than broadcast because of the modulation required for tape recording. When it comes to
DVD and other high-end recording devices, the window opens up significantly.
The rule of thumb for resolution on a 4:3 display is 80 lines of horizontal resolution for every megahertz of
bandwidth. Since DVD is capable of over 6MHZ of luminance bandwidth, you can achieve 500+ lines of luminance
resolution. Since chrominance is modulating a 3.58MHZ carrier, the bandwidth must be restricted to 1MHZ (at
least on the I channel) to keep the sidebands from spilling over and covering the entire luminance territory. Even
though the chroma is interleaved between the luminance scan lines, cross talk still occurs as the luminance
frequency nears the chroma decoder "window". Component video does not utilize the 3.58 encoding and,
therefore, is not restricted to the 1MHZ bandwidth on the chroma signal. Using the 80 lines of resolution per
MHZ, you see that a maximum of 80 lines of resolution is available for chroma.
Component video allows us to "open" the chroma bandwidth to 3MHZ, which gives much more vivid color detail,
especially at the edges of transitions. The better the display device, the more you will see this difference.
Circuit description and troubleshooting will begin with the lower-end T and S line models and then cover the V
line series. Since video processing tends to follow a predictable path from input to CRT, very basic block
diagrams will be used to isolate problems. Once the problem has been isolated to a certain area, more detailed
block diagrams will be illustrated. Even more detail, of course, can be found in the service literature.
Video problems can be divided into three distinct categories: 1) No video; 2) Improper Video Level; and 3) Video
Distortion.
S Model Video Troubleshooting
As illustrated in Figure 7-1, the main difference in this model series is the lack of a 3D comb filter, using a glass
type instead. It also utilizes a simple PIP circuit which overlays a second video source on top of the main picture.
This box can be moved around the screen and its size can be varied by the user. Since a 3D comb filter is not
used, the main video path will not be processed by a decoder circuit. Any S video sources will head directly to the
YC/Jungle IC206 after passing through some switches. The switches are necessary in order to toggle the
source of the main (or parent picture) and the sub (child picture) path. Since a component video source is
available at video 4 input, a YUV controller, IC1901, is utilized to switch the component source directly into the
YC/Jungle IC206.
The sub video path does not utilize any type of comb filtering but it does go through a decoding process by
IC1902. This is necessary since this path will enter the PIP processor, IC1905 and the 3.58MHZ carrier must be
removed. The block diagram in Figure 7-1 is rather crude but it serves its purpose well as you can get a good
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