I'll happily answer your questions, Gregg. By 1989 there were some American shows still on TV, however their popularity began to vanish around that time, since cable got more and more famous. People preferred to watch American shows with subtitles on cable than watching them dubbed on terrestrial TV, where you have to cross you fingers for the network to buy anymore more than the first season of any given series. Because of that, over-the-air TV nowadays hardly has anything American, save for Simpsons reruns.
About the news, the only channels with newscasts on weekends are channel 7 (normally a 30 minute showing on both Saturdays and Sundays around 9 PM) and ch. 2 (7 PM).
About 24-hour operation, channel 11 and 13 keep closing their programming everyday. Ch. 11 does so around 2/2:30 AM, coming back at 6 AM on weekdays and 9 AM on weekends. Ch. 13 closes around 1 AM and comes back at 5:45 AM on weekdays and 8 AM on weekends. Channel 7 still closes down once a week (early Monday morning), while ch. 2 and 9 are 24-hour operators.
We still have only 5 channels in Buenos Aires, but many parts of the country (including my town) have digital terrestrial TV. Unfortunately, while the video quality is excellent and there are new channels that aren't even seen on cable, the only network included on this service is channel 7, so we still have to resort to analogue TV (or DirecTV, in my case) to watch the other channels.
I hope I had answered your questions.