Ive just purchased my !st tig machine. never tiged before. Got the machine out of the box, set up properly, fresh bottle of argon, Began padding beads. Every thing was going well, beads were looking good. got down to about 525-550 psi argon i started getting an Green flash, erratic arc, so i turned up the gas flow, cleaned up tungsten. began running good beads again until i got to 500psi. Green arc started again erratic arc occured again, but this time couldn't fix the problem. Any suggestions.