ColecoCollector

Hello. I recently bought a collection of vintage gaming systems and I have sold most of them. The last one I sold was a ColecoVision (Model Number: 2400) bundle with all kinds of games and controllers. When I tested it, I had no problems, but the buyer is having some video output distortions and I was wondering if anyone here might know how to fix it. From his description, and the video he sent, it looks like the picture scrolls up and down the screen when he plays. He has looked at the power switch issue, but it does not seem like that is what is causing this problem. He did say that when he manipulates the video cord on the back of the console he sees more distortion, so he was considering resodering the connections. What do you all think? Thank you so much for your help. (I have attached a video he sent of what the screen looks like when this happens.) IMG_4736.mp4