*** Chapter 8 ***
When you get to the point where the basketball hoop falls through the floor, you're close to this particular TV. Jump down the hole, Kill the little creeper crawling along the floor and follow the corridor that is likely behind you at this point.
You'll come to a room with a red health station on the wall. Walk up to the station and then look to your left. Climb the ladder. You'll end up behind a blue stage curtain.
Go forward and around the corner. Open the door and you'll be in a little area with a staircase up and a staircase down. Go DOWN! If you go up you'll probably end up missing the achievement (which is what I did the first time).
Follow the path until you get to a room with a wall missing some pieces. Walk up to this wall and turn left. You'll find yourself in a nasty little room. Can't miss the TV.