I've had an rgb modified AV famicom for a few years and have never had issues. Recently the power cable I bought with it stopped working and I could tell because it had a burning plastic smell. The system worked fine for about a week but now when it is powered in video is perfect unless there is audio and then colors drop and there are red lines that flash across the screen. When audio drops lines go away. Is there something that could have blown that's causing the audio to interfere with the video?
What does it look like inside?
Never mind. It must have been interference with the cables. Everything works now what a relief.