Shredder triggers Bin Full light

My Fellowes DM15C shredder shuts off after about 4 seconds and the Bin Full light comes on. Of course it is not full. I think I need to clean the sensor/s, but I don't know where to find it/them. I took the bin out, turned the machine upside-down, held in the Bin Missing switch and ran the machine - but couldn't locate any Bin Full sensor.
I've tried looking at the Fellowes site but 1) they don't mention my model at all, and 2) they don't list fixes for any model. Perhaps I am looking in the wrong place?
Can you help?
Thanks,
Penny