I did a search on the Yahoo group Janome 6500/6600 and found an article on Jumping Bobbins (which might not be the end-of-bobbin issue, but is related to other bobbin problems that I've experienced on my 6600). I quote:
"TANGLED THREADS & JUMPING BOBBINS:
Last night I talked to my friends John and Shirley at my Janome dealer about this issue. (Please note that I have NOT had the problem - knock on wood!)
John showed me what was happening, and I'm hoping this can help those who are having the problem.
Remove the throat plate.
In the lower right corner, looking into the machine,
is a tiny guide with a spring on it. There are two arrows - when the bobbin case is in the machine, the arrows on the spring should line up, and the spring should be TIGHT. There is a Phillips screws that holds the spring in place.
If this spring is loose and is moving around, it allows the bobbin too much movement, which allows it to 'jump'. Line up the red arrows and tighten the screw. My personal theory is that some machines left the factory without having this screw adjusted properly - it is an easy fix, and if it saves
someone a long drive or shipping their machine out, that would be wondrous."
Article with pictures on adjusting bobbin case
[ATTACH=CONFIG]146402[/ATTACH]