This is a very solid model, and relatively simple since it's a straight stitcher. If there's any problem I would take out the needle plate, bobbin and bobbin case, double and tripple check parts down there, scrape every groove, corner, opening, passage, etc. with a tooth pick to check if there's any lint or grime stuck some where. That's the only tricky thing about this model, lint gets stuck in hard to reach places in the bobbin - feed dog area, and it almost always improves with that extra careful inspection and cleaning.
Another trick is to be a bit persitent; take the machine in regular use, perservere, go through all the maintanance steps and check points you can think of and you will get to the problem spot. Make sure thread doesn't get dragged down on the first few stitches of a seam or when you restart stitching after the thread has been cut. That will cause jamming. I assume you know all of this, but I swear, it's often a basic issues casing these problems.
Last edited by Mickey2; 03-01-2019 at 06:15 PM.