HP 4550 Service Manual - Page 267

Repetitive defects troubleshooting CAUTION Repetitive defects are defects that occur on the page. Most repetitive defects are caused by problems with one of the following: Table 7-8.
Developer roller
Charge roller
Cleaning roller
Transfer roller
Fuser
Imaging drum
Transfer belt See page 266 for the repetitive defect ruler and Table 7-9 for the defect spacing chart. Do not expose the imaging drum to light, and be careful not to scratch or get fingerprints on the drum surface during cleaning. Do not blow on the imaging drum. Imaging drum defects Causes:
Damage such as scratches or dents on the imaging drum. These usually appear as black or white 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 light sections in the printed output. The life of the imaging drum is shortened by exposure to light. Actions:
Print at least four configuration pages to determine if the defect repeats in the same horizontal orientation.
Inspect the imaging drum for scratches, dents, or other damage. Replace if needed.
If the problem is dust, remove the dust with isopropyl alcohol applied with a lint-free, static-free 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. C7085-90921 Chapter 7 Troubleshooting 265