sexton_mallard,
Have you given any thought as to how you will get a picture one that set once you have repaired it?
The Aurora standards converter is excellent, and works out of the box, but it is also many times the cost of your TV, and you have to make all your material available as a 625 line signal.
However, a Windows PC with the right graphics card is able to generate a 405 line output directly, and this is what I am doing here
https://www.youtube.com/watch?v=Q9b7_x0g0uM
All you need is a dual-head ATI Radeon HD 2400 Pro, and a VHF modulator, I built this
http://www.earlytelevision.org/405_modulator.html
Have a look at the posts by Peter Scott and myself in the "System converters" area of the forum, so far we seem to be the only two using this route.
Graham.
G3ZVT