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20. RA-5A Video Path Troubleshooting
Video Appears in Right Box Only: The sub-video path is working correctly. An interruption in the main video
processing has occurred. The problem is likely to be on the B board since most of the processing occurs there.
The Q Box routes the main and sub-video into the MID
TM
circuits for side-by-side display. The problem could be
on the Q board. Isolate the two by checking for video signals at CN005 pins A5, A6 and A7. If no video is
present, repair or change the B board.
NOTE: This circuit has an interesting feature that allows the user to enlarge the left or right box with the remote
joystick. When both inputs are non-HD signals, the larger box will automatically switch in the main video source.
By default, the two boxes appear equal in size with the main source on the left. If the right box appears larger
than the left, the main video signal is being sent there.
Video Appears in Both Boxes: The main and sub paths are functioning. This is the only time in which NTSC
resolution video is not sent to the DRC
TM
circuits for line doubling. The twin view signal is routed to the video
processor IC3006. The DRC
TM
is either not receiving main video, not processing it, or the line-doubled video is
not being switched properly. All of these suspected areas are located on the Q board and must be replaced as
a unit.
No Video in Either Box: If the boxes appear over a gray background, the MID
TM
circuits and the path to the video
processor is OK. The lack of video indicates a failure of both the main and sub-video paths. Since all decoding
and video switching of the main and sub paths occur on the B board, this is where the problem lies.
Video Level or Distortion: The same procedures used to isolate a no video condition can be used to locate the
source of distortion or level problems. With the introduction of multiple A/D and D/A converters and digital
processing circuits, noise in the video is likely to be more common and can take on some strange symptoms.
Fortunately, most digital noise problems have a distinct digital appearance. They may be stationary on the
screen or move around in a clock-like stepping motion. Minor or severe loss of picture detail is caused by one or
more of the parallel bit lines being inactive. The more significant the bit, the more detail loss will occur. Power
supply and external noise will “float” since they are not synchronized with the video.
Using Component Video: The use of a component video source is useful when the need arises to troubleshoot
beyond board level to a specific component. It bypasses all of the decoding circuits, thus, eliminating several
potential sources. A high definition component source is better. The DRC
TM
is also bypassed as a potential
cause. A unique feature in this chassis is the “HD Bypass” control. IC002 on the B board normally switches
video from the Q Box into the video processor IC3006. By entering the service mode and selecting category
“OP” and item “HDPT”, the data can be set from 0 to 1. This will cause IC002 to switch a
1080i source only
from
video 5 or 6 input directly to IC3006. It is a useful tool in isolating the Q Box as a potential problem source.
