Chosen Solution

Hello. I would like to have the help of experts to help me troubleshoot a broken television.This television is a TCL 55C715 UHD television and the backlight failed overnight.Observation:

  • It is possible to see the image on the screen if I place a powerful light on the screen, and the sound works.

Actions already tried:

  • Full TV reset.- Measurements on the power board: * Voltage measured on the motherboard power supply: 12Vdc. * Voltage measured on the backlight power supply: 0v. * Voltage measured from the motherboard on the “BL_ON” pin and ground: > On: 3V. > Off: 0V. (So for me, the instruction for lighting the LEDs is given….(?))

  • Testing a new power board: * Purchase of an identical card on the internet, it was received and then directly tested on the television. (No improvement). No voltage at the backlight pin outputs either.

  • I tried to power a pair of LEDs at 3.3Vdc, 5Vdc, 12Vdc with my power supply but nothing visible (screen on)

  • (Not sure of me) Attempt to measure LEDs (No resistance on the 4 pairs, between each red and black wire).

  • (Not sure of me) Attempt to measure LEDs with the “LED” mode of the tester, no result. -With an BackLight tester, I’ve try to lightup LED. Its worked ! Each pair lighting up different parts of the TV! (96Volts)

Do you have any ideas about the breakdown or suggestions for measures to be taken? Thank you very much for your feedback. Have a good day.

After making the measurements, I’ve plugged the backlight connector to the power PCB. I was surprised to see the back light working fine when I shut on the TV!

I dont know why and how the backlight worked fine. Think it the issue was solved, I reassembling the TV. However, whe I’ve rpowered the TV, the backlight where off… I’ve noticed that there is a flash when I switch on the TV:

(Little flash appear in the little hole, during maybe 0,5 seconds) When the where fine, I’ve make measurement: Between L1+ & Ground = 20mvBetween L2+ & Ground = 20mvBetween L3+ & Ground = 115VBetween L4+ & Ground = 115V I dont know why, but there is no voltage on L1 and L2. But the backlight where fully working at this point (No dark zone)

@johnythings that flash sure looks like your backlight strips failing. I really would consider that my next step.