In addition to what that guy who posted above me says. I would add bring in the thread you are using as the tech can also adjust the tension for you to give you a base point.
I have a couple of Juki Industrials and two Pfaffs. My sewing machine tech is saying there is still a strong demand for the Pfaff. He also handles Juki. Like Steve was saying they are a well built machine and parts are easier to come by.