All has been well for the most part for the first year, welding aluminum has always been a little off though and now the AC performance has taken a complete nosedive. I haven't changed settings other than frequency and it does not matter anyhow it happens from the lowest to the highest. I only use Thoriated or Lanthanated tungsten properly sharpened and cleaned. The arc is EXTREMELY unstable, I even tried using it on pulse and it made no difference. For the first 5 months I had to more or less force the arc and at higher frequency it really started to break up but now it is just un-workable. All of the basics have been checked and I have 2 other machines here ( HTP 221 and a Miller Dynasty 200 ) to compare with. Any ideas? Or should I just send it in??