HP 8550 Service Manual - Page 481

The output image is too dark Unit Printer Cause Step Density sensor 1 Grounding wire 2 contact (drum cartridge) Contact (drum 3 cartridge; for primary charging bias) High-voltage 4 PCB1 (inadequate primary charging bias) Checks Yes/No Action Is the lens of the density YES sensor soiled? Clean the lens with a special brush. Is the contact of the YES grounding wire of the drum cartridge or the contact of the drum grounding wire for the printer unit soiled? Clean the contact. If it is defective or damaged, replace the problem part. Also, check for a displaced contact. Are the contacts soiled on YES either of the following? l drum cartridge l primary charging Clean the contact. If it is defective or damaged, replace the problem part. Also, check for a displaced contact. Replace the high-voltage YES PCB1. Is the problem NO corrected? End. Replace the dc controller PCB. The copier fails to generate images Unit Copy module Cause Step 1 Checks Make a horizontal stripe test print (TYPE=10, 16). Is the image normal? Yes/No Action YES Check the connectors and wiring to the AP-IP PCB and CCD driver PCB. EN Copy module troubleshooting 479