thanks,
seeing as iv been testing without the two logic pins connected, this does not sound like this is the issue (as an aside, even with the logic pins connected, im not using 4 and 17, ive moved them to 23 and 24 using the setup file, hence why i have not mounted the shim directly).
does it matter which ground/5v pins you use?
i should be receiving a second on/off shim tomorrow which should let me know if it has been a faulty unit all along. i will report back how it goes.
cheers,
Sean