I purchased the Zenith DTT-900 DTV Converter Box from Radio Shack in May 2008.  It performed well until March 2009 when it began turning itself off after a few minutes of operation.  After resetting it, confirming the auto-off function wasn't the problem I determined the problem was heat related.  The box has been installed with plenty of air flow and unobstructed vents so I believe the issue is quality related.  I've installed several Zenith boxes, several RCA boxes, and one GE box. This is the first Zenith failure (the GE box also failed the same way in a totally different location and...