TCL 50e4900fs TV turning itself off?

[AmmoJammo]

The unit appears to match the attached PDF. Well... parts of it do. Maybe I've missed something, but the mains PSU section seems to be a bit lacking.

Nonetheless, it will power up, appear fully functional for about 30 seconds, then put itself back into standby.

All voltages appear present when its powered up.

The power supply appears to match the SHG5504B-101H schematic attached.
When the TV is powered up, "PWON" is at 2.8volts.

Any suggestions would be great!

Thanks! 

[AmmoJammo]

Photo of the dc-dc section.

[m k]

Nonetheless, it will power up, appear fully functional for about 30 seconds, then put itself back into standby.

Is timing accurate?
Could be some no signal no picture thingy.

Can you measure if some control signals are dipping before power?
Some early models were just dimming their backlights.

[shakalnokturn]

What's the supply voltage to the CPU?
If it comes from one of the 1117 linear regulators you may want to monitor that. On more than one occasion I've seen them running a little low and decreasing when warm until they would cause a hang or shut-down.

I've only ever repaired one TCL LCD TV, the PSU was similar to your schematic, there was a weak solder and arcing on a MLCC on the small 3.3V daughter board.

[keymaster]

Is the time of shut-off always the same?
Is there a difference when the tv is cold and when is harm?
If the time is always the same , then the system is failing to pass some internal test. The most common fail is the number o led, that have fail shorted.
I don't know if this model test the leds, but i have seen it in some LG and Samsung models.

[AmmoJammo]

It shuts down at the same time, every time. 45 seconds after pressing the power button, about 15 seconds after it appears to finish booting... Temperature appears to make no difference.

On the first initial splash screen, the backlight appears to change brightness, but I don't believe that's an issue.

CPU is powered by a switchedmode regulator, measures 1.255volts, but I might put a scope on it... if I can find my scope

EDIT: the resistor values used suggest the CPU voltage should be 1.18volts. 

[AmmoJammo]

Powered the main board from an external 12 and 3.3volt supplies, and it still shut down.

[Rasz]

are you connecting any external signals to it?

[m k]

VGA seems to have 3_3VSB, a wakeup?

Manual page 24 has Q001 and Q002 doing 3_3V from 3_3VSB, page 27 has reset.

Accurate timing points to an intentional operation.