I've got a 12" RGB, commonly known as an LC Monitor (the kind a shadow mask tube in place of a Trinitron), and am having some focus issues with it which seem to go beyond the internal focus knob (which I have not yet tried adjusting).

When I turn the monitor on, the focus is fine. As I leave it on, it goes out of focus. This became worse over time.

I get a feeling this has something to do with a component in the power supply. It seems to be fairly common on this model of monitor. If anyone has a guess as to what this could be and what I would need to fix it, please let me know.