Thanks for the tips, guys. I pulled the printer to bits this afternoon, and I have the mainboard from it sitting right next to me right now. Its actually a very simple design, from what I can see, there's no reed switches or anything anywhere that I can see, but there are two optical sensors on the mainboard, which are activated by the sheet feeder, at locations PS1 and PS2 on the mainboard, they're similar to the ones you'd find in a ball mouse. They look spotless to me, but still, there could be something up with them...how do you clean optical sensors?