Hi DjOMARiMari,
The motherboard for L502X may not fit in L501X system. As far as the graphics is concerned, L501X is shipped with Intel HD Graphics Media Accelerator whereas L502X is shipped with Intel HD Graphics 3000. Both the system is shipped with switchable graphics.
Hope this information helps.
Thanks and Regards,
Appu S
I have a dell xps 15 L501x and i want to upgrade to L502x.. but what i want to be sure about is, (1): does all "L502x" have 2gig graphics card on board. (2): when I buy a "L502x" MotherBoard, will any "L502x" 1080p LCD Screen works with the motherboard board i Buy?

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