Power supply caps. My 1990 27" Zenith did the same thing after sitting in a cold-ish basement for a year or so. It's the one I installed in the old cabinet, and still looks fine.
Power caps were all that ever went bad on it.
I think this is older than the bad tubes... I think those started in 1993-ish.
Mine had daily use for 10+ years and still has an excellent picture. In fact, we got my grandparents a similar 27" set around 1993-4 because ours had such a great picture... Theirs was dead within three-four years.
