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26. RA-6 Video Circuit Troubleshooting
Chapter 26 - RA-6 Video Circuit Troubleshooting
General Description
The video process circuitry in the RA-6 chassis follows a similar processing path as the RA-5A chassis with the
exception on an on-board DTV tuner and decoder. Two NTSC tuners are incorporated along with video inputs
1~4 to allow the connection of composite or S video sources. An extra component input has been added (video
6) along with video 5, to allow two sources of video up to 1080i resolution. All video sources are selected and
routed on the U board.
The A board provides the necessary comb filtering of the main and sub video along with decoder circuits to
prepare non-component NTSC sources for line doubling and twin picture processing. It also carries the video
processor for RGB conversion to be sent to the CRT drivers. The B board contains the digital processing
components, primarily the Digital Reality Creator and Multi-Image Driver.
Due to the Twin Picture feature and Component inputs, several switching stages are incorporated to alter the
path of incoming video. It is these switching circuits along with main, sub and component paths that add to the
complexity of the video circuit design, but these can be used to an advantage when attempting to isolate sources
of video problems. Even though board replacement is currently being implemented, isolating which board contains
the failure is necessary and there may come a time when component level troubleshooting is necessary due to
board unavailability.
Troubleshooting
Figure 26-1 illustrates an overall view of the video path. All composite and S video sources in the main path are
processed by 3D comb filter IC6. In the sub-video path, composite sources are sent through a 2D comb filter
IC2007. S video is passed straight through to IC306. Both video sources are stripped of sync and chroma sub-
carrier by IC303 for the main, and IC301 for the sub. The main will split into two paths, one to the DRC and the
other to the MID. Sub-video only goes to the MID to provide a second picture source for P & P and PIP.