At work I have -so far- found 7 different kind of sewing machines abandoned under the tables, on the shelves or in dusty corners. Some of them have been labelled broken and recycled. So far I have serviced and fixed 4 of 7. Three of these seven are actually so broken that they need a professional service with new parts.
See the cracked white part which has lost half of it. The lost half is mostly behind the part but you can notice it on the pic. I actually found two similar Bernette so we'll see if we can fix them both at low cost or make one whole of these two. These are old proper sergers from early 90's so they are worth of trying.
More about servicing your own sewing machines you can find on these posts:
Remember: Opening the machine breaks the warranty, you do it in your own responsibility, always plug off the machine from the power before opening it (turning off is not enough) and take pictures by your smart phone from every step you take because it helps you to put it all back!