I purchased a used 350LX from a manufacturing plant that upgraded (supposedly working good when removed from production). I've been getting it running in my shop, and ran into a problem. On DC, it welds very well on steel. I did a few tests, with different settings, etc., getting a feel for the machine, and it worked well.

Then, I switched to AC to test on some aluminum, and that's where the issues arose. Test pieces are 3/16" 6061 plate. Tungsten is a red band 3/32" dia. The torch is a Weldcraft 17, and is known good as I've used it a lot on my Syncrowave 200. I started with a pointed tip on my tungsten, and it's balled nicely in playing with it.

The first symptom is that I am having no arc stability at all. If I up the current to >150A, I can force enough heat into the part to start a puddle, but it's affecting a large area (probably nickel size or bigger). Changing the balance all the way toward penetration helps, but not enough to actually weld with it.

The second symptom is that I'm getting a white oxidation around the weld area. Using pure argon, and the flow is set at about 25, and I trust the reg/flow meter as I moved them from my working Syncrowave 200.

The third symptom is that I think it's putting too much heat back into the tungsten. If it do a fairly short test, the tungsten is red hot...

The fourth symptom is that it occasionally shocks the heck out of me through the welding table while testing it.

I'm assuming that I have some sort of issue with the high frequency system, but I need a little help / direction for where to head.