I've got a chipped Xbox with Evo-X and recently bought this YUV-Cable:
http://www.amazon.de/Component-Kabel-Optic...8138&sr=8-1
I switched to NTSC video output with the Enigmah tool and activated the HD possibilities in the original M$ dashboard.
Most games work very good and except for LOTR Return of the King (PAL) every game starts. But while playing some games I get a black screen for about half a second every 10 minutes. Could my Samsung LCD TV be the problem?

The same thing happens to me. It has happened on multiple tvs. I don't know what kind of cord I have, I've had it for years. It is annoying and usually happens at the worst possible time during the game. I've thought about buying a new cord but haven't yet. I wonder if it happens to all the cords or just the cheap ones(like what I have)