I have a Janome 9700--LOVE IT... I take it to the hospital (repair shop) annually--costs about $100.00 but she gets a good cleaning and I have never had any problem with the machine, except for the ones I cause.
I buy prewound bobbins, but rewind them onto Janome bobbins. Again, no problems.
Also, I have never tried to change the tension on the bobbin housing and keep the top tension on AUTO.
Good luck,
Barbara