This thread is great! I tried this achievement after watching all of the youtube guides and I could not get it! I thought I had all of the TVs. I tried about 5 times and failed.
After reading this entire thread, this is what I did to finally get the cheevo. This might help you if you are still having problems:
1. Read this entire thread and every post in it
2. Started the "Charlie Don't Surf" mission on Recruit difficulty.
3. I spent a lot of time in the large news room. I shot every possible TV I could find, including all of them on the walls (the rainbow ones, the turned off ones, and the ones broadcasting the terrorist)
4. In the last room with the final six TVs, I shot them as fast as possible. Somewhere in this thread that your AI buddies will shut off the broadcast, but you must shoot them before they do this.
5. Then watch the achievement pop up