HP 8550 Service Manual - Page 489

The print has white spots Unit Printer Cause Step Toner 1 cartridge Photo- 2 sensitive drum unit Secondary 3 transfer belt assembly Inter- 4 mediate transfer drum unit Secondary 5 transfer belt assembly High- 6 voltage PCB 2 (in- adequate transfer bias output)/dc controller PCB Checks Yes/No Action Are any of the developing cylinders YES of the toner cartridge defective? Replace the problem cartridge. Is the photosensitive drum or the YES primary charging roller defective? Replace the photosensitive drum cartridge. Is the unlocking mechanism of the YES secondary transfer belt assembly defective? Replace the problem part. Is the intermediate transfer drum YES unit defective or soiled? Replace the intermediate transfer drum unit. Are the contacts soiled on either of YES the following? l secondary transfer belt assembly l secondary transfer bias Replace the high-voltage PCB 2. Is YES the problem corrected? NO Clean the contact. If it is defective or damaged, replace the problem part. Also, check for a displaced contact. End Replace the dc controller PCB. EN Copy module troubleshooting 487