HP MFP P77740 Pagewide

[Lagonda]

Anybody know how a P77740 detects that the head cleaning/ wiper unit is in place?
There is a blue plastic tag on top of the wiper unit that moves as the web is used up but I can't find a sensor that monitors it.
I have one that keeps telling me to load the wiper unit but doesn't see it when I do put a new one in there.

[Lance15]

Printhead wiper

The printhead wiper system keeps the printhead nozzles firing correctly throughout the life of the printer as it performs the wiping and capping functions.
The wiping function cleans the nozzles of ink residue and particulates.
The capping function keeps the nozzles moist during storage and when the printer is idle.
The printhead wiper system uses its own motor to power the horizontal sled motion as it perform its functions.
The web fabric is on a supply reel that advances after wiping takes place. Advancing is done by backing into a stationary trigger mechanism located on the rear frame that turns a gear to advance the web. Because the web is on a supply reel, the web will eventually run out of material. The printer reports a low-web condition with approximately 12,000 pages remaining. If the sled is not replaced after the low warning is given and the printer continues to be used, the printer mechanism will reach a point where the web is so low that the unit will stop functioning until a new sled is installed. The estimated life of a printhead wiper is approximately 150,000 pages.
To perform the capping function, the printhead wiper moves underneath the printhead (which is elevated from the print position). This allows the rubber cap to seal the print nozzles from the environment.

[Lagonda]

Thanks for that Lance, but how does the copier detect if a sled is actually present?

[Lance15]

It seems there is a procedure that needs to be followed when replacing this unit. I'm not familiar with these PageWide units at all. Just trying to help.

HP PageWide Pro 750, HP PageWide Pro MFP 772/777, HP PageWide Managed P75050, and HP PageWide Managed MFP P77740/P77750/P77760 - Removal and replacement: Printhead wiper kit | HP(R) Customer Support