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:

1. Stop all Media Center services and processes
1. Close Media Center
2. Start-->Run-->services.msc (or Control Panel-->Administrative Tools-->Services)
3. Stop "Media Center Receiver Service"
4. Stop "Media Center Scheduler Service"
2. Open Registry Editor (Start-->Run-->regedit.exe)
3. Delete the key at:
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Media Center\Service\Video\Tuners
4. Start Media Center

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.