HP Color LaserJet 8500 Service Manual - Page 469

CAUTION Fuser Symptoms: Print defects occurring at about 150.5 mm. The defects will be most visible on overhead transparencies. Cause: Defect on the upper fuser roller. Actions: 1 Power the printer off, allow 30 minutes for the fuser to cool, and remove the fuser. 2 Turn the fuser gears and inspect the surface of the upper fusing roller. If the roller has surface defects, replace the fuser assembly. Imaging drum Symptoms: Print defects occurring every 195 mm. Causes:
Damage such as scratches or dents on the imaging drum. These usually appear as dark or light marks on the page.
Paper dust adhering to the imaging drum. These usually appear as white marks in the dark printed areas of the page.
Exposure of portions of the imaging drum to light. This causes dark sections in the printed output. The life of the imaging drum is shortened by exposure to strong light. Actions:
Print at least four configuration pages to determine if the defect repeats in the same vertical orientation.
Inspect the imaging drum for scratches, dents, or other damage. Replace if needed.
If the problem is dust, remove the dust with 70% isopropyl alcohol applied with a hand wipe. Try this only if the print defect is unacceptable and the only other alternative is replacing the imaging drum.
Defects caused by exposure to light might clear up over time. If severe, replace the imaging drum. Do not expose the imaging drum to direct sunlight, and be careful not to scratch or get fingerprints on the drum surface during cleaning. EN Repetitive defects troubleshooting 467