Arg...When I play NSMBU in 1080p (which the tv can handle) the screen keeps going black for 3 seconds every 5 mins or so. I called Nintendo, they think it's probably the tv and I should try it on another set first. I'll have to take it somewhere, cause I don't have another HD set.
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Maybe a bad cable or connection?
When I hooked my Macbook up to my TV at 1080 vs HDMI the TV would work fine for a while then automatically switch inputs to something else eventually. Wiggling the cable fixed it.