Thanks by explanations
Vectrexrolli and Janzl!
I just received it today
In fact the brightness potentiometer was defective This part I knew, what I did not know is that the brightness could be detrimental to the gameplay and the console.
Anyway, I opened the console and the button was there, spinning, non-stop as if dusted, but nothing happened, the glow was still strong. So I moved it gently to the left and to the right and the brightness diminished I can not control the brightness at will, but it was good to play now I've never seen a Vectrex in my life, it's really cool!