SONY KDL-55HX850 : No backlight, no error code, rest OK

[Diah]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

CN6401 pin 5 BL_ON did you have voltage on it when turn on ?

[Jojo337]

Hi all !

I got a Sony 55HX850 with psu APS-326(ch) and Driver LED ST550RD-S01.
I don't know what happenned before I get it.

The TV is working great, except the led backlight that does'nt. Backlight nevers turn on, not even a little flash.

The TV doesn't show red light errors at start The tv is working, I heard the sound of TV from antenna, menu etc... with the flash of my phone I can see the picture that seems fine (T-con OK ?).

Fuses from Driver LED ST550RD-S01 seems fine (multimeter beeping : not broken, 0V), and caps of this card too.

Pins :

If I disconnect the Driver LED cable (CN6601), nothing changes :
CN6601 pins (tested on card and psu):
TV ON :
Pin 14 : 3.3v
13 : 3.8v
12 : 0.6v
11 : 0.7v
Others : 0v

TV OFF
Pin 11 : 0.7v
Others : 0v

TV STARTING
Like ON
BUT ALL VLED_VCC (pins 1 2 3 4) go to 0.15v and go back to 0v after 4 seconds.

If I disconnect CN6401 (to the motherboard), no backlight.
If I disconnect any other cable, the error leds associated to what I disconnected appears.

CN6401 (to motherboard) pins :
TV ON : TV OFF :
Pin Pin
28 3.3v 28 3.3v
27 3v 27 3v
26 3.3v 26 0v

23 3.3v 23 3.3v

20 12.43v 20 0v
19 12.43v 19 0v
18 12.53v 18 12.54v
17 12.53v 17 12.54v
16 12.53v 16 12.54v
15 12.53v 15 12.54v
14 12.53v 14 12.54v
13 12.53v 13 12.54v
Others : 0v Others : 0v

OOF long post !! So anyway I'm in France and ... voila !
(I tried a shunt pin 5/23/28 but nothing).

Thanks for the help ! Have a good day.