HP 8550 Service Manual - Page 543

Faults not identified by error codes No power Cause Poor interface between side HCI and printer (C-link interface) Defective power switch Step 1 2 Blown power 3 supply fuse, overcurrent/ overvoltage detection circuit triggered Checks Y/N Is the power on signal being NO input? Remove the power supply NO assembly and place the tester lead pins across the power switch terminals. Check if the tester gives a reading of 0Ω when the switch is set to ON and a reading of ∞Ω when it is set to OFF. Turn off the power switch and NO wait two minutes before turning it on again. Does the unit now operate normally? YES Defective power 4 supply unit, wiring, dc load, deck controller PCB Turn off the printer assembly power switch and disconnect connector J203 on the deck controller PCB. Turn on the unit power switch and measure the dc power supply output of cable connector J203. (Be sure not to short-circuit any components at this time.) Does the J203 connector put out the measured dc power supply? NO YES Action Inspect both ends of connectors for damage. Connector the connectors securely. Replace the power supply assembly. Remove the power supply assembly and replace the blown fuse or replace the power supply. Note: Inspect the side HCI for blown fuses before replacing. Disconnect the power supply connector and connect it again. If this does not help, correct the cause that triggered the overcurrent/ overvoltage detection circuits in the power supply assembly and turn on the power again. Replace the power supply assembly. Check the wiring and dc load ahead of the deck controller PCB. If the wiring and the dc load are OK, replace the deck controller PCB. EN Side HCI troubleshooting 541