On Sunday, December 22, 2019 at 8:53:45 AM UTC-8, Michael Mud wrote:
I use a few of these boxes on older tv's. They are the ones Radio Shack sold. I like to use them with timers, which I program more than a day ahead. The a/d boxes ARE NOT PLUGGED into the timers. What I'm finding is that they shut down on their own, after sitting idle for a number of hours. Are they dependent on a tv being on to stay on? Is there a sensing circuit, or are they just old and tired. TIA.

There's a 'sleep timer' or similar named function; it can be turned off, with the menu.
The setting is intended to be nonvolatile, so you don't need to visit it often.