Apple LaserWriter 12/640 PS - Manual (Page 321)

3 Check around the roller area. You may have to push the roller to see if a paper is behind
the roller.
4 Once you have removed the jammed paper, slide the tray back into the duplex printing
unit and close the door.
5 Open and close the top cover to reset the printer.
Avoiding paper and envelope jams and wrinkling
Depending on the quality of paper and envelopes that you use, some papers
or envelopes may jam or wrinkle as they pass through the printer.
If you experience paper jams, loosen up the stack of paper by fanning it
before you load it into the paper cassette. Be sure not to overload the cassette.
With stiffer paper stock, try printing the paper from the multipurpose tray,
which provides a straighter feed into the printer than from the cassettes.
296 Chapter 12