Hey Shaun
Hmmmmm...
Have you considered you may be a Jinx?
I take it you haven't messed about in the service menu to cause the problem? From what you said it suddenly "went wrong" so I take it you didn't.
You didn't mention wether you were watching R1 or R2 DVD, but I'll assume R2. In which case can you try an R1? As I said, the convergence is held seperately for this and will give us a clue as to the problem.
The key to initial convergence is the green (centre gun) alignment. This needs to be centred on screen - hence the large green cross the full width & height of the screen, and the little notches in the exact centre of the case. The red & blue guns can only be adjusted so far in relation to the green centre gun, at which point the guns cannot be adjusted further. Do you have the ability to move the green cross at all? Once this is in place, look at the red, then the blue. The blue will never sit entirely behind the cross (and be hidden) but will always "bloom" a little around the edges. This is to do with the tech, full explanation not required (cos I've forgotten for the minute).
In theory, you should be able to purchase your TV, take it home and watch a perfect picture. In practice, the factory only sets up the TV to "within tolerance" and this may not give perfect results - hence the need to "tweek" the picture a bit yourself (assuming you want the best results!).
You will find this is not only an issue with RP sets but with direct view and projector as well. Unless you want to shell out for a plasma, there is always a going to be some slight tweeking. The manufacturers even recognise this, that's why they put "convergence" options in the user menu's.
OK. It may be that you are unlucky (Jinxed?) enough to get another duff set in which case a swap will be necessary. It's worth a try in getting that green gun alligned first. Let me know if you can move it at all.
Cheers
Laurel