Sharp tv shows no picture, but indicator light is lit.

[royzhero]

I acquired a free 50” TV. IT is a Sharp LC50LE752E. It does not show a picture.

When power is plugged in, the indicator light will turn on, the backlight stays off and nothing is visible, even with a flashlight. When pressing the touch buttons on the tv nothing happens. When pressing buttons on the remote control the indicator light will blink indicating the IRsignal was received, but nothing happens.

Out of the 20 times that I have booted it, it did turn on 3 times and stayed on. It then showed a ‘No Input’ screen with a perfect screen without glitches. After powering it off and on again with the power button, then it would not show a picture anymore.

Troubleshooting:

All power supply connector voltages are normal, except there is no backlight_on voltage. Standby power is 5 v
Return power from the main board to trigger the power supply board is 3.5v.
Manually shorting the Backlight on with the Power supply on lights the backlight normally and will stay on as long as I short it.
I have reseated all connectors going between the boards.
I have tried to find out why it did boot sometimes, but have not been able to. Have tried pressing on the main chip for example.
The main board is DUNTKG135FM08. The power supply board is RDENCA459WJQZ.

Board diagrams in PDF:

https://1drv.ms/b/s!AkpE6xgs6VHNhGNwakvV...

I am guessing there is a problem with the main chip or the standby chip IC3800. I’m not sure where to go from here. Any help is appreciated.

[m3vuv]

firs thing i would do is measure the esr of all the caps in the psu.

[Alex Eisenhut]

First thing I would do is enter that model into YouTube. Touch nothing, listen, and learn first.

[royzhero]

Thank you both for your replies.
I have checked all diodes and capacitors on the PS board. All diodes are one-way and all capacitors show acceptable ESR.

I have been able to turn it on yesterday. I plugged it in and the it started booting after 5 or 6 seconds. Then I was able to get into settings and into factory settings (by pressing MENU and slowly pressing 9 9 9 2 2 2) and was using and scrolling through the menu for about 15 minutes. I then left it on but discovered after 10 minutes that the screen had turned off again while the power led was still blue (it will turn red on standby), and I was not able to do anything but take the plug out again.