Jammed mechanism - Bernina 827?

I had just started sewing a new seam. Some of the loose threads (Attached to the material) were caught up in the movement of the needle and got pulled into the bottom section of the machine. They came out when I removed the material, but now the wheel turns only with great reluctance and a lot of pressure. The 'jam' appears to occur when the bottom mechanism is moving. When this occurred in my mom's old Elna, I could just lift the bottom cover and remove threads which were caught there. I don't know if the same thing has happened with this machine, but I am unable to open the bottom section to check. Any ideas? Having used the old Elna all my life, changing to the Bernina is like changing from a Manual to an Automatic car!