M17XR4 sent to tech support, now something is missing! Help me recognize the part.

Hi guys,
a few days ago i sent my m17x R4 because the HDMI out port was not working properly.
Actually i sent it another time before because the gpu was not working properly (I was getting the VIDEO_TDR_ERROR non stop). They changed my gtx 675m and when i got it back the HDMI port wasnt working.

Now that i got it back for the second time i noticed something different inside, when opening the back cover. The modules circled in red in the photo are gone, now there is just the empty slot.
I always thought that it was the RAM, but windows does recognize 8gb installed even if that slot is empty.
The report sheet that came with the laptop says: Replaced parts: MAINBOARD SVC, PWA, THERMALPAD, ANW, M17XR4 T9CPM
Maybe they installed a different motherboard and now the RAM is somewhere else?

Please help me in recognizing this part, i had bad experiences with the European Alienware/Dell assitance (i'm from Italy). They even damaged the back cover and now it doesn't close itself properly! I am scared they forgot something while reassembling the laptop

photo:

 

You should have 2 more ram slots under the keyboard and they might have put your ram there.

Does windows and bios report the same amount of ram?

 

Thanks for the reply, yes like i said windows and bios report 8gb ram.
While checking the bios i noticed that there are 4 ram slot, 2 empty and 2 with 4gb ram. So i guess it's ok?

 

It's ok, they have been installed under the keyboard.

 

I'm happy with that. Then I have another question. Can I just buy a compatible ram module and install it in the empy slot?

 

Yes you can. Try matching the RAM with the one you currently have for better results.

 

Thanks for the replies, case solved