Sound, But No Picture?

Hello! I'm fairly new when it comes to diagnosing issues with CRTs. I picked up a 1992 GE 20GT360 from my local recycling center and was hoping to add it to my collection. It turns on, shows the channel number and I can navigate through the menus to adjust sound and video, but when I plug in my n64 all I get is sound and no picture. I checked the connections on my wires and everything is good. Tried the old jiggle trick with no luck. I know it's not my n64, as it works fine on my RCA. Any ideas, or am I taking this back to the recycling center?