I also have a 205 but with a different problem (see shop talk).  Are you using a foot pedal?  I am assuming so since you said it happens on AC as well.  There are several parameters that can be set on the machine that aren't so apparent.  If you have a manual, it will describe them.  If not, go to Lincoln's website and download a manual.  You have to hold down the parameter select button when you turn on the machine and it will allow you to set various "fixed" parameters i.e. waveform shape, touch start or hi-freq, preflow, start power, etc.  I would start there.  These are wonderful little machines, but a little sensitive I think...