Apple LaserWriter 12/640 PS - Manual (Page 225)

Checking the indicator lights
The lights on the front panel of the LaserWriter 12/640 PS indicate the
printer’s operating status.
Light On Off Flashing
Ready/In Use Printer is ready Printer cannot print Printer is warming up,
to use. because of an error, printing a startup
or the cover is open, page, or processing
or the printer is data for the next
turned off. print job.
Paper Out Paper cassette Paper supply is OK. Printer is ready for
is empty. sheet of manual-feed
paper.
Paper Jam There is a paper Paper is OK Toner cartridge is.
jam. not installed.
If the Paper Out and Paper Jam lights flash alternately, or all three lights stay
on, the printer requires service. If you have just installed additional memory
(RAM) in the printer, there may be a problem with the memory. Open the
printer and make sure the SIMMs are fully seated in the correct sockets that
match one of the supported configurations listed in Chapter 5 and in
Appendix D.
226 Chapter 11