Canon C3500 - Manual (Page 250)

If you are using the BC-21e Color BJ Cartridge and your output is
blank, one of the BJ tanks is probably out of ink. See the instructions
starting on page 9-16 for replacing a BJ tank.
The following procedure describes how to replace the BC-21e Color
BJ Cartridge with the optional BC-20 Black BJ Cartridge. Follow the
instructions in this section to replace an old BJ cartridge or to change
BJ cartridges when you are switching between the BC-21e and any of the
optional BJ cartridges.
You only need to replace the BC-21e Color BJ Cartridge when the print
head is damaged (or after printing approximately 2000 pages). If one of
the BJ tanks (either color or black) in your BC-21e Color BJ Cartridge is
out of ink, see the next section (page 9-16) for instructions on how to
replace a BJ tank.
To replace the BJ cartridge, follow these steps:
The cartridge holder moves to the center
of the unit.
❍ Grasp both sides and lift it up. Open the
printer cover.
Press the
CARTRIDGE
button.
9-12 Maintaining the MultiPASS C3500 Chapter 9
DO NOT TOUCH THE
RIBBON CABLE
DO NOT TOUCH THE
GUIDE RAIL
DO NOT TOUCH THE
ROUND SHAFT