if you turn off the power  to the hob, (make sure its off) take out the hob turn it up side down, take the back off" unscrew it , off. you can take out any ring, for replacemant , take a photo of the wireing  camera/phone. so you know what it looks like , take out the ring see the power out put stampeed on it , get a ring with the same power ,they will know at any good electrical  store. or get one on line for it ,  not hard to replace once you can get the back off the hob , , just make sure all the power if off when working on it . and you be fine .
                 mark
                
 June 2010