Convergence is the adjustment by which a monitor or TV properly overlaps the 3 separate red, blue and green images to produce a proper color image. It applies to all CRT based TV sets and monitors except those using a single image forming module for all 3 colors (e.g. DLP and most (but not all) LCD projectors, and LCD and plasma screens). Normally there are two steps, the first is "static convergence" in which the 3 images (red, blue and green) are adjusted to overlap at the exact center of the screen. The second is dynamic convergence in which the rest of the screen is "converged". Note that "perfect" convergence is generally not possible, but modern devices get very close. Also note that on some newer CRTs, some or all of the convergence adjustments are fixed at the factory and cannot be adjusted. Static convergence is usually adjusted using magnets on the CRT neck (again, common practice today is that these are set at the factory and then epoxy glued). Dynamic convergence is complex, if it's adjustable at all there can be as many as 30-40 controls effecting different colors in different parts of the screen. You also need a test pattern generator to make this adjustment (although on a computer (vs. a TV), you might be able to do it with a black screen and the letter "H" in various places). I can't give you any help for your specific device, you need to locate a service manual or you probably won't be able to do much with it.