Have a HP 4000n printer, was reading up on if there isnt a paperjam it could be a stuck sensor. Is there anywhere listed that shows a picture of where that "sensor" would be ? Also, i am wondering if the pickup rollers need to be cleaned too ... once it tries to print, not to sound trivial , but its making a very odd groaning noise and then I get the paper jam error. Most of the time, the paper doesnt even leave the bottom tray. Not being a printer repair person ... I would need to try to find a diagram so if I rip this thing apart and order parts I can figure out how to put it back together. Any advise ?