Samsung QN55QN90AAF backlight blinking.

[Roach182]

Hi, I could not find any threads that already described this problem so I am starting a new one.

The back-light on this TV blinks on and off at random times depending on the brightness. At max brightness in blinks steadily, at minimum brightness it rarely blinks. All picture enhancement options and eco options are turned off. The voltages from the PSU board are all good. I did notice a Film cap (1uf 600v) on the PSU that gives a faint click each time the back-light blinks. I replaced it but the problem remained.

TIA for any help.

[Diah]

Re: Samsung QN55QN90AAF backlight blinking.

At max brightness in blinks steadily, at minimum brightness it rarely blinks.

you have bad LED BL

[Roach182]

Re: Samsung QN55QN90AAF backlight blinking.

Maybe multiple bad back-light LED's then? I tried the TV with each of the back-light ribbon cables off and the result was the same. Is it possible to replace the back-lights on a QLED, I have replaced them with success on a regular LED TV.

[Diah]

Re: Samsung QN55QN90AAF backlight blinking.

Maybe multiple bad back-light LED's then? I tried the TV with each of the back-light ribbon cables off and the result was the same. Is it possible to replace the back-lights on a QLED, I have replaced them with success on a regular LED TV.

try to disconnect the mainboards from the power boards. and turn on see if the BL stay on

[Roach182]

Re: Samsung QN55QN90AAF backlight blinking.

When I disconnect the power to the main board I still get random but steady blinking. Same when I leave the PSU connected to the main board but take the data cable off that goes to the LED driver board.

[Diah]

Re: Samsung QN55QN90AAF backlight blinking.

can you show us the PSU of BL section from the top and downside ?

[Roach182]

Re: Samsung QN55QN90AAF backlight blinking.



Here is a pic of the boards

[Roach182]

Re: Samsung QN55QN90AAF backlight blinking.

Thanks for the help Diah, is it a picture you are looking for?

[Diah]

Re: Samsung QN55QN90AAF backlight blinking.

i would change the LED driver boards at the middle where LEDs connected to it. we dont have the diagram of it.. to trouble shooting it
because you said before over all LED cable when you disconnected was the blinking there...

[Roach182]

Re: Samsung QN55QN90AAF backlight blinking.

The trouble remains regardless of what combination of LED ribbon cables I disconnect. I will see if I can source an LED driver board at a reasonable price.

[Diah]

Re: Samsung QN55QN90AAF backlight blinking.

The trouble remains regardless of what combination of LED ribbon cables I disconnect. I will see if I can source an LED driver board at a reasonable price.

take it out and inspect it carefully of caps leak or BGA.../ joint connection.

[Roach182]

Re: Samsung QN55QN90AAF backlight blinking.

Thanks Diah. I will do that and report back.

[Diah]

Re: Samsung QN55QN90AAF backlight blinking.

Thanks Diah. I will do that and report back.

by the way.. this board content part of firmware ... if its corrupted, could do this issue and more dim zone..
try to log in service menu... and from there make hard reset.... or upgrade or downgrade to rewrite this firmware parts.

all of this three trying steps , the boards should be in place and all cable connected.

[Roach182]

Re: Samsung QN55QN90AAF backlight blinking.

I checked the board under a digital microscope and did a factory reset from the service menu and the trouble is still on.