Epson Stylus Photo R300 false 'paper jam error' !

[leo0306]

Hi all,
Does anyone have, by chance :-), the service manual for Epson inkjet printer Stylus Photo R300? I receive a false 'paper jam error' and I can't print anything, but the nozzle check pattern comes out perfectly. I've tried all tricks I've known several times (uninstall printer, change driver, change USB cable, change USB port, change cartridges with new ones, even format partition and reinstall OS). I think it is a sensor problem or printing head (it might require cleaning or resetting somehow), but this is only my opinion, I’m not a specialist in service for printers. I'll be very grateful for any kind of help!
BR,
Leo