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Sorry missed the other. Other components:
Direct TV box with DVR
DVD/SmartTV box (Sony)
Both the DirectTV box and the SmartTV box produce the issue whether both are powered or or not or whether they are selected as the source or not
So I will try the backlight suggestion. As I mentioned in the what have I tried section above I did in fact try the power cord disconnect idea without result. One interesting though maybe coincidental symptom, the width of the dark spot is almost the exact width of the "information" feature of the Direct TV features. Also, it appears on about 70% of the right side of the screen. Does any of this give you any additional ideas?