Samsung NeoQLEd QA55QN85AAKLXL backlight failure

[Vdaimo]

Hi everyone,

I’m not an experienced TV technician, but I do some basic electronics repair as a hobby. I’m a mechanical engineer by profession and have experience with soldering PCBs and working with ESP32 and STM32 embedded systems.

I have a 4-year-old Samsung QA55QN85AAKLXL Neo QLED TV. Recently, the backlight stopped working completely. The TV still boots normally — I can tell the LCD panel is working and the TV functions otherwise seem normal — but there is no backlight.

Here’s what I’ve checked so far:

• Power supply board outputs around 64–65V to the LED controller PCB
• LED controller PCB also shows around 64–65V on the test pads
• No visibly burnt components
• No swollen/puffed capacitors

At this point I’m not sure how to proceed with the diagnosis. Could the issue still be failed LEDs/backlight strips even though voltage is present? What should I check next?

Any guidance would be appreciated. Thanks!

[EazyBone]

Pictures of the led driver also. Get a close up of it to see any test points

Some Samsung's have bad led drivers. It's not out of the question that a zone of leds went bad either. Mini led hard to test LEDs without taking the thing apart (that I know of)

[Vdaimo]

Thanks for replying.
I tried disconnecting led ribbon cables of each zone one at a time. Still doesn't work.

[Vdaimo]

Thanks for replying.
I tried disconnecting led ribbon cables of each zone one at a time. Still doesn't work.

[EazyBone]

Disconnecting each ribbon won't diagnose it for you.

Somehow need to test the leds