You can't take the back off.
It's probably the element.
If you tip the machine on it's side & remove the base(4 screws) you'll see the element with 2 thick cables. Pull the cables off & insulate them.
Re-fit the base & try the machine again. If it doesn't now trip, then you'll know it's a faulty element.
They cost about £150.
Bernii
January 2011