I need to narrow things down a little - is it the drive PSU upsetting the BOB or is it the BOB PSU ?

The BOB pulls 150mA including the three sensors.

Will be back soon with some results, the BIG worrying me is the radio interference - the plasma is fully grounded etc and works perfectly BUT it pumps out RF like billy!

Maybe I need to ditch the SMPS's and go linear.

Off for some tests.....