Picture Problem with the Zenith

[mwplefty]

I just hooked up the APEX converter box to the 1976 Zenith 4-Tube Hybrid. I turned it on to channel 3, scanned for channels, and all was well. (The colors were a little messed up but that was the least of my worries at the time). I watched it for about 30 minutes or so and turned it off.

Just for fun, I thought I would turn it back on again, and this was when the picture crapped out on me. The sound was perfect and the channels were changing fine with the remote, but the picture wasn't showing up. It wasn't snowy or anything like that. It was just black with several white lines running horizontally up and down the screen. I adjusted just about every switch on the outside of the set, fixed the rabbit ears, but nothing worked.

Could it be as simple as just adjusting the AGC switch? I doubt it's the converter box itself considering that I still get sound and the remote is functioning properly. Or maybe I was watching it too long and it just needs to sit for a while?

What does anyone think?