I've done composite video mods for my Genesis and my SMS, but when the screens go black and come back with something on the screen, the screen always bounces once. During normal gameplay the video is fine, it's just kind of annoying to see this in places such as in-between levels, or during cut scenes.
So, for example, it would happen where like the Sega logo comes up (both systems), then screen goes black, then when the title screen comes up, the video scrolls up very fast exactly one screen and then the video stays... then I start the game, screen goes black, then when the first level comes up the screen bounces/scrolls again, and is fine until the next black screen.
Any ideas as to what could be causing this? This is also now occurring when I use the built in AV out ports on both systems, which is wear I'm pulling the video and ground signals from. It's not a major issue, it's just kind of annoying.