Samsung UN60H6300AF no backlight, brief flash at power up

[gustagen]

Hi All, I've had some great successes with repairing several displays with the help of the members here.

I'm currently troubleshooting a Samsung UN60H6300AF with a backlight issue. Upon powering up, the backlight flashes once for a fraction of a second. I can see the on-screen display with a flashlight.

I've attached photos of the PSU board, and can provide more photos if needed. I have an auto-ranging DMM and very basic knowledge of circuitry.

Can someone recommend the tests used to determine if the problem is either the driver circuit or the LED strips themselves? Should I reference chassis ground when measuring voltages at CNL802? Thank you for any help you can provide!

[Davi.p]

Re: Samsung UN60H6300AF no backlight, brief flash at power up

Hi, i'm not usual at backlight repairing, keep in mind that this poblem relies 99% in the leds, so if you repair very occasionally so go and open the screen, if you are searching a better test i guess you can build a simple led tester with 1 diode bridge, 1 power resistor, two tester cables and another diode, there are plenty of these projects on YouTube, doing this you will test bl from the PS output cables, if it doesn't light up or the tension read on the bl cables is lower than the one printed on the psb then leds are faulty. This is not much precise if you have only two output cables but if bl (backlight) is Split in 4,6,more cables, by comparing their tensions if them are different so led fault.

[handsworth]

Re: Samsung UN60H6300AF no backlight, brief flash at power up

First I would do the flashlight test and see if an image appears thru the dark screen. If you see image, then its faulty backlights. Second test would be to unplug the AC power. Then unplug the cable that connects the power supply to the main board. Replug the AC power. Backlights should come on instantly. If they dont, I would suspect backlights again.

[Davi.p]

Re: Samsung UN60H6300AF no backlight, brief flash at power up

First I would do the flashlight test

already done.

Second test would be to unplug .....

second test unuseful in my opinion, seen the previous test result.

[neilc6]

Re: Samsung UN60H6300AF no backlight, brief flash at power up

If you want to repair TVs, you need to buy a backlight tester. LED failure is the most common problem in LED TVs.

[Davi.p]

Re: Samsung UN60H6300AF no backlight, brief flash at power up

But are we sure that instrument is mandatory for few tv? Lets say if leds are bad, the power supply is ok, so to avoid searching for led driver controller schematic and a protection bypass, one reads the data table printed on board , only bad chinese all in 1 board don't have it, if you read Vmax,Imax, make V/I you found a resistor value to put from led return wire and ground, you can test leds without other devices, i think 1/4w can suffice..

[neilc6]

Re: Samsung UN60H6300AF no backlight, brief flash at power up

OP has encountered backlight issues at least three times before. Just looked at that second thread and I recommended he buy one there as well.

https://www.badcaps.net/forum/showthread.php?t=72752

https://www.badcaps.net/forum/showthread.php?t=71390

https://www.badcaps.net/forum/showthread.php?t=79109

[Davi.p]

Re: Samsung UN60H6300AF no backlight, brief flash at power up

Two tv are few ware, the backlight tester must be used in some way, or if not it doesn't reveal many times a faulty led set because led all light up..

[neilc6]

Re: Samsung UN60H6300AF no backlight, brief flash at power up

With known models and symptoms, I don't test LED strips anymore and just replace them all with new. However with a LED tester, I can drive the LED strips independent of the power supply and check the TV turns on, has video, and doesn't have panel damage before spending money on new strips.

Note OP's original problem - backlight issues are almost always the LEDs themselves. Samsungs don't have protection shutdown unlike almost every other manufacturer so on Samsungs, bad backlights can damage the power supply.

[Davi.p]

Re: Samsung UN60H6300AF no backlight, brief flash at power up

The task you are telling is done by an old mains cable, diode bridge, resistor, diode, output cable..