TV won't stay on for more tha 10/15 seconds - if that

To disable the Demo mode, perform the following:

1. Turn on the TV.
2. Simultaneously hold down the Vol+ and Vol- buttons on the front of the TV. Do not use the remote control.
3. Hold for about 6 seconds
4. Certain model TVs may turn off, others will not. But in either case, the Demo mode should be disabled.

Greetings,

Check first the auto-sleep timer (just in case).

If the TV turns itself off - like the power had cut-off, better check the power source if it's ok, else it would be the power supply section of the TV. If you have the tools check the output section with a meter.

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It is most likely a protection mechanism which turns the tv of incase there is a electrical problem inside. I would really suggest that you contact a local repair man and have the set checked.