I don't know how the 400 works, but on my 100, a red light will come on when powering it and will stay on for a full minute, then will turn green, meaning it's ready to use. It is clearly described in the owner's manual. Hopefully that's all it is.
Straight out of the box doesn't work.
Just received my new Prima Luna EVO 400. Heavy thing, looks good. Took the foam off the tubes, only on the power tubes. Nothing on the small tubes. I'm new at this, don't know what they are called. I did notice some of the tubes were a little crooked so I seated them in a little better. However ( you new that was coming) two of the small tubes on the right kind of wooble. Did I spell that right? What the hell plugged in and red light on the right side. It doesn't work right out of the box. Going back tomorrow. Just wanted to let ya know. Going to go through the recommendations again. Good night.