When it switches off, does it go back into standby mode and you have to turn it on or does it restart by itself?
If it goes back to standby and stays there until you turn it on again, then it sounds as if something is overheating and it is shutting down.
If it restarts by itself it could be a loose connection (dry solder joint?) or a voltage problem perhaps
Here’s the relevant troubleshooting flowchart from the service manual which may be a good place to start. (see p.26 also)
I don't know.
It may also be software related.
Just to eliminate any possibly corrupted software, try a power refresh to hopefully restore any corrupted software.
Turn off the TV if on and disconnect the power from the TV.
Press and hold the TV Power on button for a full 30 seconds and then release it.
Reconnect the power to the TV and turn it on and check.
Not hopeful about this but still worth a shot as it doesn't take long ;-)
If still no good try to update the firmware
My thinking on this is that it seems with your TV that it looks for the file on the USB port soon after it starts and obviously since most times it is not there it progresses through the startup sequence of the software already installed.
If it does recognize the USB and stays on and gives onscreen instructions etc to load as described in the firmware instructions I linked then it may be that the firmware already there has a problem and hopefully this will fix it.
The caveat is that if the TV already has this firmware version installed usually it may not re-install the same version again. A lot only "update" to a later version if you get what I mean.
If it fails to recognize the USB etc then looking at the manual (see p.33) it may require software diagnosis to check if some things are working or not so I don't know.
Sorry I can't be of more help.
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