Janome memory craft 6500 sewing machine...all of a sudden, the bobbin thread does not attach itself to the needle thread...i have taken off the plate, cleaned out the dust, rethreaded both top and bottom threads, changed bobbins...still doesn't attach...do I need a new bobbin case?

Has the bobbin case dislodged and moved? there should be two red marks one on the bobbin case and one on the outer holder, are they lining up? Sometimes as these cases are held by a magnet, they will get dislodged and move slightly, especially in a jam up.
Take out the bobbin case and clean under it, then replace it matching up the red marks.



If the bobbin case has actaully been struck by the needle during a dislodgement, it may well pierce the bobbin case plastic, look for burring or marks on the outer flange area. If this has occured, the thread may catch on the burr as it comes over the bobbin and jam again.

You can buy a new bobbin case if yours is damaged or maybe just file the burring with an emery board (remove it from the machine first of course).

Lastly, check your needle hasn't been bent, burred, or put in backwards, any of these can prevent a stitch from forming.

If all the above fails, then it is possible that the timing has been knocked out and you will need to get it serviced by a technician.