I have a jvc 27 inch tv I picked up and it has bad convergence on the top and bottom of the screen. Is this something I need to adjust using the rings?
The yoke wedges or am I lucky enough maybe the service menu will fix this?
If convergence is out of whack uniformly on the screen, adjusting the yoke rings will help. However, if everything lines up in the center as it should, you need play around with magnets and permalloy strips (yoke tabs).
EDIT: actually, when you say it's bad on both the top and the bottom, the yoke could be misaligned. Take a picture showing the whole screen.