Samsung UN40H5203AF LED backlight blinking

[imaddicted2u]

Samsung UN40H5203AF LED backlight is blinking on and off. Set doesn't turn on.
If I unplug the LEDS from the power LED driver board, the set turns on, has sound and it passes the flashlight test.
On the BN44-00769C Power Supply / LED Board shows the LED supply voltage should be 151.8v at 425ma with the LEDs connected but I can't get good measurements on the LED connector with the LEDs blinking.
With the LEDs disconnected the open circuit voltage on pins 1 and 2 (D+) to chassis is 211v.
I thought I'd post to ask if the problem is more likely to be the LED strips or the Power Supply / LED Board.

[imaddicted2u]

Re: Samsung UN40H5203AF LED backlight blinking

Here are a couple of pics of the power LED board.

[dick_barton]

Re: Samsung UN40H5203AF LED backlight blinking

Your results do tend to agree that it's an led problem. Is it' possible to reduce the backlights and see if they then stay on?

[Andrew F. Ali]

Re: Samsung UN40H5203AF LED backlight blinking

The only long term solution is to replace the LED Backlights. Not just the bad strip but ALL the strips to prevent having to open up the Panel multiple times.

[imaddicted2u]

Re: Samsung UN40H5203AF LED backlight blinking

Your results do tend to agree that it's an led problem. Is it' possible to reduce the backlights and see if they then stay on?

Thanks,
Good thing my main tv is Samsung and the menus structure is nearly the same. I was able to feel around with a flashlight until I found the backlight setting. It was at max = 20. I turned it down to = 5.
It made a difference. The backlights still blinks but stays on for a split second longer so the display can be seen.
https://i.imgur.com/0uPxsrE.mp4

[neilc6]

Re: Samsung UN40H5203AF LED backlight blinking

I think you need to invest in a led tester. The newest models can be set to a couple hundred mA. On Samsungs, there is no protection circuitry which causes almost all leds to burn out and can also damage the power supply.

[budm]

Re: Samsung UN40H5203AF LED backlight blinking

https://www.badcaps.net/forum/attach...9&d=1570706323
Lift up one leg of diode D9801C and check RESISTANCE in both directions.

[imaddicted2u]

Re: Samsung UN40H5203AF LED backlight blinking

https://www.badcaps.net/forum/attach...9&d=1570706323
Lift up one leg of diode D9801C and check RESISTANCE in both directions.

Looks like a good diode. On ohms 1.9Mohm one way, open the other. On diode test. Forward bias one way, open the other way

[budm]

Re: Samsung UN40H5203AF LED backlight blinking

Good, if that diode has leakage it will also cause the backlghts flickering. LED tester at this point will help narrowing down the issue.

[imaddicted2u]

Re: Samsung UN40H5203AF LED backlight blinking

Here is a look at inside the panel...I guess this answers the question...
https://i.imgur.com/RMglmFj.mp4

[budm]

Re: Samsung UN40H5203AF LED backlight blinking

Replace all the strips at the same time.

[imaddicted2u]

Re: Samsung UN40H5203AF LED backlight blinking

Replace all the strips at the same time.

Correct me if I'm wrong, all the LEDS are in series? if one LED was open, none would light...right?
Thanks as usual, budm, That's the plan, the bottom strip must have all LEDs shorted. The other two strips have a few in each shorted...The video doesn't do it justice, some of the LEDs blew pretty violently.

[dick_barton]

Re: Samsung UN40H5203AF LED backlight blinking

If an led along a stip burns open circuit then all remaining leds along that strip remain off. If a led along a strip shorts out then the strip will continue to work but the remaining leds will be running harder which then leads to multiple failures.

If strips are connected in series then the above remains true replacing strip with strips.

[neilc6]

Re: Samsung UN40H5203AF LED backlight blinking

There is an open led in the chain as well as the shorted ones. If all shorted, they would all progressively fail and the screen would get dimmer due to lack of protection shut off.

[imaddicted2u]

Re: Samsung UN40H5203AF LED backlight blinking

There is an open led in the chain as well as the shorted ones. If all shorted, they would all progressively fail and the screen would get dimmer due to lack of protection shut off.

Hate to argue but current cannot flow through an open LED. Once one LED goes open none of the LEDs connected in the series chain would be able to light.

[neilc6]

Re: Samsung UN40H5203AF LED backlight blinking

You have six wires going to the series circuit. Each string is getting power. Every tv is wired a bit differently.

https://www.badcaps.net/forum/showthread.php?t=70123

[imaddicted2u]

Re: Samsung UN40H5203AF LED backlight blinking

Ok, are you saying each of the 3 strips are in parallel, with the leds on each strip being in series. If that was the case then an open on one strip would only affect that strip.
I haven't seen a circuit diagram for this set but others I've looked at had all the LEDs in series and the strips were either jumped to create a series circuit at the power supply connector or inside the panel. Given the led power supply voltage involved I figured all the leds were in series.

[neilc6]

Re: Samsung UN40H5203AF LED backlight blinking

They could be all shorted or one could be open in the string. That's where an LED tester would come in handy. Doesn't really matter since you should replace all the strips anyways.

[budm]

Re: Samsung UN40H5203AF LED backlight blinking

The three LED strings are connected in series to form one large LED string (you can see how they are connected by looking at the bottom side of the LED connector), you have lots of shorted out LEDs.