Hardware 3DS upper screen dim (dark) but image (screen content) is there.. Why?

[hama364]

Dear all,

bought this 2nd hand 3DS in very good condition, however...

the screen is dim = dark when looked at straight. When I view from an angle I can see the (expected) screen content, so it seems the screen is somewhat working...

Does this mean the back light is broken?
Can it be fixed without exchanging the whole screen, e.g. re-seating cable or other "trick"?
If not can the back light be exchanged separately or only with the screen itself as a whole assembly?

Thanks and have a nice day, Mike