HP Deskjet 3520 Inkjet Printer - Manual (Page 19)

ink-backup mode
Ink-backup mode allows the printer to operate using only one print cartridge. It is
initiated when a print cartridge is removed from the cradle.
For instructions on removing a print cartridge, click here .
ink-backup mode output
Printing in ink-backup mode slows the printer and affects the quality of printouts.
when only this print cartridge is
installed...
the result is...
black print cartridge Colors are printed as grayscale.
tri-color print cartridge
Colors print but black is grayed and
is not a true black.
exiting ink-backup mode
Install two print cartridges in the printer to exit ink-backup mode.
For instructions on installing a print cartridge, click here .