HH LaserJet MFP479 - Black Display after Fuser Unit Replacement - What to Do ?

[PatrickJP66]

Hello !

I am writing from an offshore installation in Iraq where I am working.

This is about a repair tentative on a HP LaserJetPro MFP M479fdw (220-240v)

Product No: W1A80A

Serial No: [Personal Information Removed]

86,500+ printing cycles approx.

Operated on genuine HP 415A Toner cartridges (no aftermarket/reconditionned) and Double A Premium A4 paper.

We had a damaged fusing unit: pressure roller coated with printed matter and plasticky film plus a sheared piece of paper stuck between the fuser / pressure roller. The pressure roller contamination/damage left undesired imprint on all printed materials until printing stopped due to the paper jam.

Following HP procedure / YouTube videos, I have replaced the damaged fusing unit (200v Ref: RM2-6435 3VN 8410129433/White bar code label) with genuine HP replacements procured in Dubai, UAE (Ref: RM2-6435 3VN 8430092113/Pink bar code label), I have also cleaned the fans. I took care that the electro-magnet fork be properly aligned with the white pivot allowing the flap actuation as necessary.

Upon turning the machine ON, the Display remains black, the machine status remains Offline, the start routine goes through with the 3 engines spinning on the side, the bottom fan then top running alternatively with the bottom fan remaining ON thereafter.

From the ethernet cable connection network the printer status always shows Offline irrespective whether power is ON or OFF.

I have tried to unplug the ethernet cable and power cable, wait 60+ seconds, reconnect the power cable to no avail as the printer only repeats the same start routine but the display remains unpowered black... Done same procedure plus pressing the power button for 20 seconds whilst disconnected from power then reconnect the power cable. It did not work.

Questions:

1) What shall I do next ?

2) Could a diagnostic be established using a USB or ethernet cable connected to a PC ?

3) We have a multimeter, are there any test points to be checked for further diagnostics ?

4) Could it be that these new fuser units require different firmware / software loaded into the printer so that the Display lit up again ? In such case from where could this be collected and  how could this be loaded into the printer ?

5) On one video I noted that the pressure roller should rotate smoothly. The damaged one rotates smoothly but both the two new ones are much stiffer to rotate but these do rotate. Is this normal ?