TV is 18 months old
Turn it on, blue power light is on, the backlight comes on, it shows the SCEPTRE logo on the screen for a few seconds, and the source input picture shows for about 1 second, then the TV turns off.
When it goes off, the power light goes to red (this is off/standby), so it's not just losing backlight.
When the power is on, blue light, the 5V and 12V on the power supply are good. The 24v to backlight is good. The 5v Standby power is ALWAYS good. When the TV turns off, the 5V and 12V and 24V go to 0, but the Standby 5V stays up... that's all good.
If I force the power supply's 24v outputs on, by connecting "STB" pin (that is the power on pin) to "5V Standby in, then the backlight comes on and stays on, the power supply never turns itself off, and the 24V stays at 24V. Of course, the TV itself isn't powered on at this time, but it shows the backlight and power supply is good.
So, I am pretty sure that the power supply is fine, and it is that the TV main board is telling the power supply to shut down after a few seconds (using the power supply's STB (power on) pin.
I unplugged the backlight from the power supply, and it still has the same symptoms (except of course the backlight doesn't come on at all with it disconnected).
All capacitors look fine, and like i said the power supply appears to be testing fine.
There are 2 wires coming from the inverter board back to the main board (not the power supply). I think these wires tell the main board if the backlights are functioning so it doesn't keep running the TV if the backlight is not firing.
I measured the voltage across those 2 wires coming from the inverter board while the backlight was on, and while it was not connected to the main board, and the voltage is 0.7 volts coming from the inverter board. I imagine that number should be higher. Perhaps not all of the backlights are working, or maybe the circuit that sends voltage back to indicate they are working is not working. There are 10 backlights, and I can see the 10 transformers, but I don't know how to tell if they are all working since I can't actually see the backlights.
What should that voltage be to indicate to the main board that they are functional? How can I test if each light is working?
Turn it on, blue power light is on, the backlight comes on, it shows the SCEPTRE logo on the screen for a few seconds, and the source input picture shows for about 1 second, then the TV turns off.
When it goes off, the power light goes to red (this is off/standby), so it's not just losing backlight.
When the power is on, blue light, the 5V and 12V on the power supply are good. The 24v to backlight is good. The 5v Standby power is ALWAYS good. When the TV turns off, the 5V and 12V and 24V go to 0, but the Standby 5V stays up... that's all good.
If I force the power supply's 24v outputs on, by connecting "STB" pin (that is the power on pin) to "5V Standby in, then the backlight comes on and stays on, the power supply never turns itself off, and the 24V stays at 24V. Of course, the TV itself isn't powered on at this time, but it shows the backlight and power supply is good.
So, I am pretty sure that the power supply is fine, and it is that the TV main board is telling the power supply to shut down after a few seconds (using the power supply's STB (power on) pin.
I unplugged the backlight from the power supply, and it still has the same symptoms (except of course the backlight doesn't come on at all with it disconnected).
All capacitors look fine, and like i said the power supply appears to be testing fine.
There are 2 wires coming from the inverter board back to the main board (not the power supply). I think these wires tell the main board if the backlights are functioning so it doesn't keep running the TV if the backlight is not firing.
I measured the voltage across those 2 wires coming from the inverter board while the backlight was on, and while it was not connected to the main board, and the voltage is 0.7 volts coming from the inverter board. I imagine that number should be higher. Perhaps not all of the backlights are working, or maybe the circuit that sends voltage back to indicate they are working is not working. There are 10 backlights, and I can see the 10 transformers, but I don't know how to tell if they are all working since I can't actually see the backlights.
What should that voltage be to indicate to the main board that they are functional? How can I test if each light is working?