Evolution Post Filter Cover...
$6.99
Product details
The Bernina 6100 uses its own post filter cover knob, in black, Evolution part 01-7887-01. It is not the same knob as the 6400 and 6600 use, so order by model.
The knob holds the post-motor filter cover closed. When it strips or cracks, the cover sits proud instead of clamping down, and two things follow: the filter is no longer held squarely against its seat, and air finds a path around the edge of it. The machine keeps running and sounds fine, which is exactly why this gets left for months.
Threading on a new knob pulls the cover flat and puts the filter back in the airflow where it belongs. Take the filter out and look at it while the cover is off; it has been running unclamped for as long as the knob has been broken.

