XBR-75X940D : Alive but no Backlight, Seeking Advice...

[willis6732]

Hello, Tv Has no Backlight (or Sound that i know of)

Tv Turns on flashing Orange/Green, and then turns to white with remote and can be turned on and off.
Was also able to update firmware with no change.
The TV had a Burnt LED Driver IC on the Main Power board, Both main power boards have been replaced.


I would like to test the backlights on this TV without opening it up. I am confused by all the ribbon cables coming off the LED Driver board
I have a LED Tester...


Ribbon cables E,F Look totally different than A,B,C,D,G,H,I,J

I tried to probe around with beep mode to find any ground near the ribbons cables and i did not...


I dont want to damage anything...If i dont get help here then i guess the next step is to open the panel or order a replacement LED Driver board...

Thanks for any help in advanced...
KW

[Davi.p]

This is a local dimming set, the leds are controlled individually or in a short set, this means each channel is outputting very low voltage, thus i don't know how do you refers for burnt led driver ic on the main psb, can you fire out a photo of both replaced boards? You cannot test all the led channels because is not needed, it high unlikely so a few leds can block the entire set. The first thing to do is to test the couple main board / lcd panel, to do it you can watch the screen with a flashlight, but i guees you have not an image, a faulty backlight might be indicated by a status led error code. The amber green indication instead is commonly a bad pairing mb<> tcon, if none of them are been replaced, then there is a bad tcon, check its fuse or presence of input power on it

[Diah]

NOTE: I have removed the offensive opening line from this post.

you have 8 strips ABCD GHIJ . each strips had 2 zone so all in total are 16 zones , E & F are LED + which they are connect to current limit R sync , each are provide 8 zones

even you will test with LED tester you will not able to remark if they lit on.. cause of the limit counts of LED units at different position.

disconnect the ribbon cable between MB and LED driver boards will guide you if they all will turn on... in case the main boards send BL_on to PSU

NO sound mean too Optic audio port not lit on red,,, this case says MB didn't start high complete.

work around disconnect the Bl_ON cable from PSU socket and connect the pins of it with Power--on via 1KR

[willis6732]

Hey thanks guys...

Re: Davi.p
Ive never seen any picture even with a flashlight. No sign of backlight on the back or if i push on the panel. I can investigate the Tcon more...

Re:vDiah
""disconnect the ribbon cable between MB and LED driver boards will guide you if they all will turn on... in case the main boards send BL_on to PSU""
This Model has a DPS board between the MB and LED Board. If i unplug DPS to LED board there is no sign of backlight
and actually yesterday i had accidentally left the DPS to LED board unplugged whe i went to update it. Not sure if that helped but it seem to update doing quick white repetitive blinks...

"work around disconnect the Bl_ON cable from PSU socket and connect the pins of it with Power--on via 1KR"
Im guessing you meant BL-ON? There is a BL-On line going from the Right side Power board to the DPS board. and a BL-ON line going between the 2 power boards.
I can try that... Feed the DPS board BL-On signal with Power--on via 1KR...

See picture:
The power supply board on the Far left has a "Boost 1channel white LED Driver for large IC" on the back of it. This IC was burnt and left burn marks on the frame too...

Thats why i am messing with the LED driver board now, cause i thought this burnt chip was a clue to look that way....

PS: The LED Driver board has a green LED that flashes 7 quick 1 long.

[Diah]

you need to disconnected the one i remarked with red. and on the PSU socket after you disconnected simulated stand alone test , standby 3.3V with 1KR to power_on and T-con_con and BL_ON you may have other label printed

[Davi.p]

_--------------
to the OP: first, wow, what a beast of tv set, i love these ones with high complexity..
one thing i do not understand, the datasheet says DCDC converter but i see no one of these on that board, it is a ACDC PS with PFC, i see also an intermiddle board called FRC, before the tcon, one has to check voltages on it, first input 12v, then step down dcdc (on the coils), eventually linear dcdc, the supposed error code blink on the led board can be a broken led board, or a broken main board that cannot communicate with that, the STM32 microcontroller seems to have function (at least diagnostic), you might have to check one by one those lot of 4 pin ic that resembles dual mosfets, the input rail is the same, it's enough one shorted that the power rail is down.. question: the burnt ic you say was on the primary or secondary side of board?.. well, with pink hearts painted on the boards, i think one female baby tried to repair the thing... i joke..

[Document Archive]

Davi.p - I see who started the argument (which i have now deleted) but please do not respond the way you did. Instead email the admin.

[Davi.p]

Ok moderator sorry i will do..
----
to the O.P. .... i have never opened such a beast, i think the backlight is organized like this, it has the huge amount of 1024 led, wow, wonderful ------ (i don't recall the term), them are organized in a grid of 64x16 and are controlled one, or 16, per time in sequence, the sot23 ic are probably dual protection diodes, i don't know if them have to be checked each one, one leg is gnd, the other two must not be gnd otherwise are at fault.. the gnd leg could be the one near the vias because the other two are on the traces of the led channels..

[willis6732]

work around disconnect the Bl_ON cable from PSU socket and connect the pins of it with Power--on via 1KR

you need to disconnected the one i remarked with red. and on the PSU socket after you disconnected simulated stand alone test , standby 3.3V with 1KR to power_on and T-con_con and BL_ON you may have other label printed

Thank you for the instructions. I am not super clear on the second instructions, but ive got as far as i could understand.

To clarify more the symptoms are... when pugged in, no light for 10 seconds (Except Green LED on LED board), then orange-green alternating, then 10 seconds later the remote works and the light turns to white and the light can be turned on and off with power button on remote.


I unplugged the 3x connectors that you marked with the stars in image... and same symptoms

Next I cut the BL-ON wire and connected the the DPS/MAIN side to a 1K and then to POWER_ON.
(Shown in Pic)

The connector also has:
TCON_ON
STBY_Voltage

It sounded like you were saying i could grab power from either POWER_ON or STBY_Voltage
What do i do with STBY_Voltage?

And i think you were saying i shloud also apply power to TCON_ON with a 1K resistor as well..

Not sure if that is correct or not.


I've included images of all the connectors on the PSU boards

I appreciate your time in helping out.
Thanks again
K

[Diah]

apply hard reset to the set via the TV keys