The TD-15 and TD-11 contain an "Auto-Off" feature which shuts down the power automatically on the module after it has not been used within a specified time. This feature can be useful to save power in case you forget to turn off the power manually. From the factory, the Auto-Off feature is set to 30 minutes.
Here's how to disable this feature.
1. Press MENU.
2. Press the cursor up or down button to choose "Options."
3. Press the function 3 button (ENTER).
4. Press cursor down to select "Auto Off."
5. Turn the dial to choose "OFF."
6. Press EXIT when you're finished. The new setting is saved automatically.