I know I'm a little late to this party, but for anyone who may stumble across this... Open your browser on the 3ds, and plug in the following website:
http://www.lagom.nl/lcd-test/black.php
What you'll do is count the number of "blank" spaces, until you begin to see solid, more tangible squares.
An IPS screen will begin to show around 8, and a TN screen at about 4.
I have two systems, myself. The silver MH4 edition, and the purple Galaxy one. Both have IPS top, and TN bottom. I've heard of people swapping out their TN screens, with a bit of technical know how.... Though I can honestly say, it doesn't make a huge difference. My original 3ds xl was dual TN, and I never even noticed until I bought the new ones. Anybow... Perhaps a bit more winded than I anticipated, but there you have it!
Hope that helps anyone who may be unsure.