HP 8550 Service Manual - Page 479

The output image is too light Unit Copy module Printer Cause Step 1 2 Black toner 3 cartridge High-voltage 4 PCB 1 (inadequate black developing- bias output) Secondary pre- 5 transfer charging assembly Intermediate 6 transfer drum unit High-voltage 7 PCB 2 (inadequate pretransfer charging bias output) Checks Yes/No Action Make a test print in service NO mode (TEST > PG > TYPE=14), YES and find the color that is light on the copy. Does the color appear on the test print? The problem is with the copy module. Go to step 2. If the color is black only, go to step 3. See "Image fault troubleshooting" on page 462. Are the contacts soiled on YES either of the following? l black toner cartridge l black developing bias Clean the contact. If it is damaged, replace the problem part. Also, check for a displaced contact. Open the front cover while NO black toner is being developed on the photosensitive drum (about 30 seconds after the start of test printing), and take out the black toner cartridge. Then, take out the black toner cartridge and check the toner image on the photosensitive drum. Is the black toner image fully developed on the surface of the photosensitive drum? Replace the high-voltage PCB 1. Is the charging wire of the secondary pre-transfer charging assembly inside the intermediate transfer drum unit broken? YES Replace the secondary pre-transfer charging assembly. Are the contacts soiled on YES either of the following? l intermediate transfer drum unit l secondary pretransfer charging bias Clean the contact. If it is soiled or damaged, replace the problem part. Also, check for a displaced contact. Replace the high-voltage PCB. Is the problem corrected? NO YES Replace the dc controller PCB. End. EN Copy module troubleshooting 477