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No backlight, no display, has sound

Hello, I have a Sony XBR-55X850C and I have no backlight, no display but I do have sound.

When I first turned the tv on it flashed 6 red LEDs. Looked up the code and it said it could be the backlights or the main or power supply board. I opened the tv up and seen that the main board was getting voltage for a few seconds then shutting off. I disconnected the T-Con board, the backlights came on. It was displaying a series of colours. I turned the tv off and plugged the T-Con board back in. When I turned it on the LED say there bottom was flashing between Orange and Green, indicating it needs a firmware update. Followed the instructions on the Sony website for updating with a memory stick. It does say to follow the instructions on the screen (can't do as there is no display) . If I press the power button I get a white LED to come on, still no display or backlights. The 6 red LEDs have not come on since. I tested the backlights and they still work. Unplugging the T-Con board doesn't display the colours either.

Below are the voltages I'm getting with the power on.

Backlight 1+2 68V

1- NC - No Pin

2 - DC_dimmer 0V

3- BL_ON 0V

4 - PWM_DIMMER 0V

5 - STBY_3.3 3.47V

6 - BLINKING 0V

7 - AC_OFF_DET 3.48V

8 - BL_ERR 2.5V

9- POWER_ON 3.4V

10- GND - n/a

11- GND - n/a

12- GND - n/a

13- REG12V 12.6V

14- REG12V 12.6V

15- REG12V 12.6V

16- REG12V 12.6V

17- REG12V NO PIN

18- REG12V 12.6V

19 - GND n/a

20 - GND n/a

21 - GND n/a

22 GND n/a

23 GND n/a

24- TCON_ON 0V

25- TCON_VCC_12 0V

26- TCON_VCC_12 0V

27- TCON_VCC_12 0V

28- TCON_VCC_12 NO PIN

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Tyler Saboe  the backlight voltage seems a bit low. you’ve tried shining a flashlight beam at an angle to see if you can make out silhouettes etc.? If you do not then the issue is more likely the t-con board , main board and power board/backlight array last. Follow the flowsheet to see what you can find out.

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Yes I have tried the flashlight, no image shows up that I can see. Do you know what the pin “BL_ERR” means? I am assuming it is backlight error and also assuming that the mainboard is throwing that error. Would the T-Con board make the backlight not come on. I'm new to how the process works, AC comes into PS sends standby signal to the main board (3.3V). Mainboard is now in standby mode waiting for a “on" signal, once it sees the “on" signal it sends a signal back to the PS via “BL_ON” pin and turns the high voltage on. Do I have that correct?

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Essentially yes. The T-con board can prevent the panel from coming on via the main board. As your voltage shows your BL_On does not show any signal. Did you check the voltage on the IC as suggested on the flowsheet?

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I did it a few weeks ago and it read high (over 3V) I have been playing with it since but haven't measured the voltage again. If it reads high again, any idea what that next step actually entails? Those acronyms don't mean anything to me.

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Tyler Saboe if it is high you may have issues with a bad ribbon cable but ultimately a high voltage on the IC is listed as a bad main board.

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@oldturkey03 Ok i will see if I can find any any ribbon cables and price out a main board. Do you think it will be the ribbon cable from the main board to the T-con or from the T-con to panel or both?

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FWIW, I re-tried the firmware installation and my TV came back from the flashing green and orange/amber light. and no picture/no backlight but with sound. I tried it when I first got the flashing lights, but there was no change.

Then looking at the voltages, I wasn't getting correct standby voltages(there was always full power going to all the boards regardless of whether indicator light was on/off) - indicating the TV was "doing something" else.

So I retried with the same USB stick and it just worked the second time. Still need to replace the T-Con board to resolve the flicker, but I do have a picture, and I didn't have to replace the main-board or backlight.

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