Removing an oven extractor hood fan cover

[Rollerball]

My canopy extractor hood isn't sucking as well as it should but I'm currently stumped how to remove the plastic fan cover. Details as follows:

The canopy extractor is a 20 year old Hygena APP 2300

I can't find a photo of the whole unit but the horizontally mounted cover under the whole unit looks like this:

https://www.amazon.co.uk/SPARES2GO-Silver-Diffuser-Hygena-Cooker/dp/B01N5Y48J6

that's easy to unclip (I've replaced the filter too).

and the round plastic fan cover I'm trying to remove (also horizontally mounted) looks like this:

https://www.buyspares.co.uk/cooker-...6271&shop=hygena&path=358051&model_ref=559129

(not a great photo but it's the best I can find)

it has four screws, these are easy enough to remove. However, despite the removal of the screws I still can't remove the cover. Looks like there are some plastic clips but what's really holding it in place seems to be where there is a raised plastic part covering the wires from the nearby lights and fan speeds control switches.

Has anyone any experience with removing one of these?

I'd like to check that the fan is in one piece because, despite it turning on and making a lot of noise, the suction is pretty weak.

 

[BlueLoo]

Perhaps it is not supposed to come off?

Certainly, that is how my Fan works. You split the casing but one side of the fan is unmountable as the cover is bonded in.

 

[Rollerball]

Well it's certainly loose when I remove the screws and at least part of it seems to be clipped (plus the part that's being stubborn moves a bit too). I'm pretty sure it should come off (plastic cover I'm trying to remove is usually screwed to the metal part of the hood).