In some cases you may find that ATSC (HDTV) no longer works after uninstalling Media Center Rollup 2 from your computer. The issue is caused by a schema change in the Tuners registry key. Today I identified a workaround to get your ATSC back up and running without reinstalling Symphony or Rollup 2.
To restore your ATSC functionality in Symphony:
This has not been rigorously tested, and has not been "officially" released to the Microsoft Knowledge Base yet. I am fairly confident of the fix, but this is posted AS-IS, with no warranties.