I have random black screens with gamecube games, the problem vary to game to game, for example en Metroid happen almost every time i go to the menu and in the console menu is when happen the most.
i upload a video with the problem:
Just an update to my last post, I tried using my mClassic with my TV as I was using just a gaming monitor with built in soundcard and speakers to play on and the black screen issue went away. I tried all of the games that were causing the issue as well as the PS TV black homescreen that would flicker and it works without a problem. I would suggest using a different TV or monitor and see if that solves your black screen issues.
I'm thinking the issue has to do with settings from the TV because my monitor has very few settings whereas my tv has plenty of them. Happy I was able to figure out the issue with mine and good luck to everyone else out there.