Wont stop running (by 2 users)

My Ativa DQ80M would run for about 2 minutes after it was done shredding. I cleaned it out thoroughly to no avail. Then I took the whole thing apart down to the activator switch. I was looking for an optical sensor (it doesn't have one).
Inserted paper moves a small plastic piece. This piece squishes a small plastic diaphragm which activates the ON switch. As the diaphragm returns to its original size, the ON switch is deactivated and it stops running. I think the plastic diaphragm is old and just not as "springy" as it once was, so it takes considerably longer to return to its original size.
To fix, I filed down the hard plastic piece (the one that paper moves and which squishes the diaphragm). I estimate that I took off a couple of millimeters. Actually I took a little off, put it back together, took it apart, and took off more.
I took off the five screws on the bottom (probably voiding the warrant), removed the plastic cover, removed the blade roller mechanism (just lifts out, no screws). Then I removed two screws to remove the plastic switch housing. The hard plastic piece lifts right out to be filed.
The end result is that the diaphragm isn't compressed as much and doesn't need as much time to return to normal shape.

Mine wouldn't stop either. Removing the shredder head off the wastebasket and looking at the shredding teeth revealed the problem. The teeth were mangled and severely bent and overlapping one another in the center of the teeth-bar. Paper was compacted in that area and the build-up made the shredder to run continuously when the power switch was on. I have the Activa DQ61BA from Office Depot. It has been used maybe 20 times at a seasonal lake home (really sparse use). It has shredded maybe 1 credit card and 10 staples on paper (which it is claimed to be ok). Since the problem is in the center of the teeth-bar, it must have been the one credit card that destroyed the cutting teeth--or else just bad design.....So much for Activa....