Lexmark T420 User Reference page 73

b
Slide the print cartridge into the printer until it snaps into place.
4
Close the upper front door.
Make sure the door snaps closed on both sides, or the printer will not function properly.
5
Turn the printer on.
6
Follow the instructions on the new print cartridge box to recycle the used print cartridge.
When you return a used print cartridge, you contribute to a worldwide recycling effort at no cost to you.
For best results, use Lexmark supplies with the printer.
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