A defect in the conception of the BROTHER TN-315 cartridges could give you problems when changing them. A quick look at the cartridge rack before closing the printer can prevent any difficulties. The easiest way to avoid problems is to close the printer gently after replacing the cartridges. When you slam that door shut, the cartridges could move and make it impossible for the printer to see they are there.

This short video (in French) shows you how to make the replacement without any worries.