If you're determined to use pneumatic cylinders, look at the ones for Mini-van rear doors. My Ford Freestar uses two, one on each side. I am sure the door weighs more than 80 pounds, and from closed to open is more than 90 degrees.
It raises the door with minimal effort. Closing the door takes minimal effort, too, but you can't just "let it go". It won't SLAM down, but it will close hard enough to latch. On your TV stand, you'd just have to make sure you had hold of it all the way down.
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