OK - Think I've fixed it. Although the form casing etc look similar. The Zif connector on the Mach SSD is the other way around- i.e. Pin 1 of the ribbon cable is at the other end. So I had to turn the whole SSD the other way up. This in turn caused the disk to be about 2mm out of polace which meant I had to cut away part of the rubber vibration housing. (I fugure there is no vibration on an SSD so that should be OK. Problem Solved.