HP Color LaserJet Enterprise CM4540 Service Manual - Page 74

Laser/scanner failure The DC controller determines that a laser/scanner has failed when any of the following conditions occurs: ● Laser failure: The detected laser intensity does not match a specified value when the product initializes. ● Scanner motor startup failure: The scanner motor does not reach a specified rotation within a specified period from when the laser scanner starts driving. ● Scanner-motor abnormal rotation: When a specified BD interval is not detected during a print operation, a BD error is determined. If the BD interval does not recover within a specified period after the BD error occurs, the product determines a scanner motor abnormal rotation. The laser/scanner system does not have a mechanical laser shutter. For safety reason, the product has a interlock switch. The interlock switch is turned off to interrupt +5 V power supply to the laser/scanner system, when the front or right door is open. Protective-glass cleaners Each laser/scanner has two openings which allow the laser beam to pass to the surface of the photosensitive drum. These openings are covered by protective glass. When the protective glass gets dirty (for example, by paper dust or toner) a protective-glass cleaner (PGC) cleans them. NOTE: When a glass is dirty, streaks appear on the printed page in the process direction. The PGC is a cleaning pad which slides along the laser shutter. With the front door open, the laser shutter is positioned over the glass. As a print cartridge is inserted, the cleaning pad is pushed down and wipes the glass. When the front door is closed after cartridge insertion, the laser shutter (and PGC) move away from the glass which allows the laser beam to pass through the glass. When the front door is opened, the laser shutter and PGC move back into position over the glass. When the cartridge is pulled out, the cleaning pad is returned to its starting position at the front of the cartridge opening. 22 Chapter 1 Theory of operation ENWW