Chromacolor II blooming issue

[AndyMack]

Ok... I've got two sets down right now (other is a roundie), trying to get the easier of the two fixed.

It's one of the Zenith Avanti series, circa 1974 (?), white with the rosewood top, not a remote set. This TV has the following numbers on the sticker on the back cover, Model E4760, chassis 25EC58 (it's really faded, best I could make out). The chassis itself says 25EC83, looks original but who knows. This set was a one-owner, who claimed it was a good TV that only required a new CRT sometime in the late 80's.

Works well but the picture has a blooming issue, where the image gets larger with increased brightness, seems to go out of focus a little and whites will smear when the contrast is turned up to what would otherwise be a normal level.

I'm not very educated when it comes to TV repair, so I thought I'd pose the question here. Is this a simple module(s) replacement, or do I have to dig into the circuitry to fix this problem.

This set also has a noisy transformer (you can hear it hum when the room is quiet). Related or no big deal?

I love this TV, has great color and a sharp picture when bright/contrast is turned way down. Any advice is appreciated as always!