NetdudeUK,
I'm not saying this to be nasty or anything, or to discourage you from repairing things, but there is a reason many in this thread have been telling you to just bin this PSU. IT is NOT a quality made PSU, no matter the branding on it. You only need to look at the supply to see that. Things you would look for in a quality supply is input filtering with inductors, X rated and Y rated capacitors, and some protection circuitry, of which this has none, bar a fuse - which also happens to be in the neutral line. If that fuse blows, the unit could still be live, and KILL YOU. It is a danger, and a fire hazard.
I do commend you trying to fix things, but please also learn when it is worth fixing something, and when to just burn it with fire. Do yourself a favour, and strip it apart, salvage the good components for you to play around with in low voltage projects, and buy yourself a quality PSU which won't kill you if something goes wrong.
I only say this in the interest of your own safety.
Theres many videos about on PSUs and ones which are dangerous. Here's one example.