The shop couldn't find the original transformer (they just swap the keyboards into a 'live' testing station) so they gave me a generic transformer that I could set the voltage to. After three hours on the internet, pushing two in morning, I changed the setting from 12v to 9v and all worked fine.
Phwoar, it's a cracking little synth. It's also my first 'proper' keyboard (my other being a Technics home keyboard - but hey, it's good enough for the band!). I believe, overall, that I got a good deal.
Bearing in mind, it's ex-demo and barely used, I snapped it up for £379 plus a free phono cable to get it into my amp. The shop sells these from stock at £439.
I'd first seen the X5D in a music store in Birmingham and they were going for £399. I picked mine up in Exeter some 120 miles away (assuming you're not from the UK here).
Think I got a good deal? It's a smashing piece of kit! I get more and more impressed each time I discover something fancy that it can do.