I came across an Atari 2600 yesterday, and everything works on it except the screen rolls very quickly and constantly. I've tested it on multiple televisions, and replaced the computer<>tv switch with a phono>coax adapter. I've tried connecting it to a tv with a vertical hold adjustment. Little better, but still rollin'. I've checked the bottom of the console, and it's not a PAL unit, and all my games display in color.

I figure the system is not properly outputting vertical sync. Does anyone know if there is a particular capacitor or transistor I can replace to try to fix the problem?