Thanks both. PSU could be an issue, I have a spare one, will try using that for the mount, with the dome on the present supply. The dome motors are on a PWM soft start circuit, so should not be too bad.
Will check secondary lockdown screws, but why am I not seeing any motion with Gurley ignored.
Next clear night, I'll try running PHD with corrections off, to see the effect clean.
Keep suggestions coming please, I really want to get this sorted, I've invested a whole lot of time in this mount, and its so close...