False ADF jam on HP Laserjet Pro M570dn

Hi,

I've recently got a second hand laserjet pro m570dn with an issue with the adf.

After start procedure, it says "Remove paper from document feeder".

Done this :

1) I've checked for paper or debris : I cannot see anything (I've rolled a paper manually through it in case of hidden paper piece).

2) I've disconnected / reconnected the adf from the printer : no change.

I haven't found any online guidelines to troubleshoot that myself so here I am asking about help on this :

- if there if one, where is the paper sensor that triggers this false alert ?

- do you know how to unmount the adf to have a look inside the mechanism ?

- could the printer be wrong about the origin of the issue ? ADF is not cheap so if I buy a new one, I'd better be sure of the issue.

Thanks in advance,

Regards,

Mikael

Mikael