Follow up: I've been able to gain a somewhat stable game state by setting up a fan to blow into the PS3. I guess that the problem is related to older "fat" PS3s not cooling well or something of that nature. I recommend trying that if you have a fan available. It is a 75% solution and the screen still goes black on me sometimes, but I have been able to finish all of the lv 50 dungeons using this method. Give it a shot.