Dell 5110cn Color Laser Printer - Manual (Page 291)

CAUTION: Do not touch inside the printer with your hands. Some parts may be hot. Allow
time for the printer to cool before attempting to remove parts in this area.
Gently wipe the automatic density control (ADC) sensor window with a clean dry cloth or cotton swab. 4.
NOTE: Do not allow anything hard to come in contact with the automatic density control (ADC) sensor
window. Do not use excessive force to clean the window.
Replace the transfer roller. Grip the tabs as shown. 5.