Considering the Bernina 830 is a very sensitive machine (I have a 830LE) I would ask the service tech to set it up & put it thru all stages while you watch. Say you want to make sure you are using the machine right. Ask questions as you go ...like threading, bobbin, embroidery, BSR, different stitches, etc. Try different threads & needles. Ask him to show you how to clean it & oil it. Take fabric along to sew on & make sure you have some big enough to fit the large hoop for embroidery a few times. Also take ALL your bobbins along & have them checked for worn paint. If they are worn this can cause the machine to not function right. Bernina is supposed to replace them for free, if the paint wore off, as it was an issue a while back. One more thing the 830 requires it be level on your sewing table or this could throw the timing off.