No color (including test page), color laserjet - m479fdw

[JFBVQS]

Printer, purchased new several years ago, has never printed color, including the demo test page.  My fault for not addressing during warranty period, but I'm dedicated to resolving this issue, but could use some expertise.

Cartridges all factory HP and recognized.  Firmware updated.  Factory resets performed. 

Color is enabled and not restricted in printer config.  I've set to B/W only, restarted, and returned to color with no change. 

I've run color calibrations at least 4 times in a row on a number of occasions with no change. 

The test page prints black only, but as if it were going to be color.  It isn't converting to grayscale. The test page is different when set to color vs black only; the black only setting gives a grayscale complete image, but color setting yields page that has black but is missing colors.

I've marked gears on all toner cartridges. They move.

I do have 2 errors:
54.11.03 - Yellow density range error.
54.14.00 - color plane registration sensor error.

Because it isn't actually printing color, I suspect these errors are likely a result of the underlying problem and not tied to the cause. I could be wrong.

The diagnostic pages also have no color.

In reviewing schematics and the imaging process, along with reading the full set of error codes, I'm wondering what behavior a defective SW2, the developer alienation switch, would cause. This switch plugs into J211 on the Driver PCB.

I've had suggestions to replace the formatter board, main engine board and the driver board. I'm tempted to shotgun and replace all, but have concern it could be this microswitch.

I've been inside the unit, but not far enough to have located this switch location to be able to test it for continuity.

Does anyone have any insight or advice? It's already been into a factory authorized repair center and they gave up. It seems that there were a batch of these defective from the factory based on some of the online reviews.

Happy to provide any further info to anyone willing to provide input. Thanks!

[NC77]

Looks like you have performed a very thorough troubleshooting process.  Congrats on your effort.

The printer can print in full-color mode or in black-only mode. To print in black-only mode, the printer disengages
the developing rollers in the cyan, magenta, and yellow toner cartridges, which maximizes the life of the
cartridges.  The developing-roller engagement and disengagement control operates as follows: When the printer is turned
on and when each print job is completed, all four of the developing units are disengaged from the photosensitive
drums. When development is not needed, a special cam mechanism on the developer roller stops the rotation
separate from the developer disengagement cam, providing even more life for the cartridge.
● The drive of the developer disengagement motor rotates the developer disengagement cam.
● As the cam rotates, the developing unit engages with or separates from the photosensitive drum.
When the print mode is full color, the developing units engage with the drums. When the print mode is blackonly, only the black developing unit engages with the drum.
The DC controller determines a developer disengagement motor failure and notiƭes the formatter when it does
not detect a specified signal from the developer disengagement sensor during the developing unit engagement
and disengagement operation. 

I would look at the transfer belt before replacing any PCBs.

I am not a HP representative.

[Repairatrooper]

Troubleshooting guide for this device states the following

For the 54.11 error, you should replace the transfer belt first and it that does not resolve the issue, replace the density sensor RM2-7399-000CN.

However for the 54.14 error, the only recommended step is to replace the density sensor so, in your shoes I would replace that first.

As you will note, this part has been replaced/updated so it is possible that first generation parts have an inherent defect. The 010CN at the end of the part number indicates this is a revised part. The original part ends in 000CN. 
Screenshot from the HP parts store.

[JFBVQS]

I appreciate your time and input.  

If you are inclined, I'm curious about your thinking on the ITB.  

I have visually inspected, and I have zero issues with black.  Can you help me understand how the transfer belt itself could cause this?  Please understand, I'm asking to understand, not disagree.

Thank you! 

[JFBVQS]

Thank you for your response.

This is 2 for 2 on ITB, so regardless whether I understand how this could be contributing to the issue, looks like I'll get one of these ordered.

Interesting info on the density sensor revision.

Here was my theory on the errors.  If the printer had no internal catch to throw an error, the calibration and density error could possibly be from having no color to "pick up" on during the calibration scan.

I just don't see any evidence the color toner cartridges have done anything other than spin. It looks as if no colored toner has ever been transferred.  This is what has me stuck understanding ITB or color calibration sensor being the cause, but the news of the updated model likely means I'll pull the trigger.  You've given me things to ponder and try.  

Thank you. 

[JFBVQS]

Had a little more time to digest your reply.

Do I understand correctly that the YMC alienation switch (SW2) is the logic source for the engagement and disengagement of the color developing unit?   If so, I believe I saw (not thrown on my printer) the errors related to the engagement of this motor, and if the motor was bound with resistance, but what would happen if the switch was bad?  It's a 4 wire connector, so is it possible this switch failure could result in uncaught errors?  Could it be that it is fully engaging and disengaging, but the switch isn't confirming (and no error would be caught)?

I'm clearly at or beyond my understanding of the interplay between the mechanics and the electronics of how this thing works, so please let me know if my question/wiring theory is completely off base.  

I need to go read more to understand how the transfer belt and the cam systems work together and how a transfer belt failure could lead to the results I'm seeing before asking anything further.

Thanks again!