Zenith pic problem

Someone has offered me a 1966 Zenith color set (sounds like a portable, don't know the size or model number yet). He describes it's problem thusly:

"I plugged it in the other day and the volume came on, but the screen was mostly dark with mutli-colors in the center."

I know that it's a long shot diagnosing something over the internet, but does this sound like a common problem, or one common with Zeniths of this vintage?

Thanks!

Anthony