Bad led strip Samsung UN55D6000SF

[gavric]

Hello, you guys helped me last time with westinghouse with bad builtin tcon.

Now i am working on samsung UN55D6000SF led tv which had blinking red light and after reading posts from others and answers to them i figured out that it had bad led strip. after cutting led strip connector wires i got one side of screen to light up by connecting black wire (negative side) to chassis of tv-blue goes to its place on ps connector and it powered on and works. Tv is almost perfect(one side darker but not too bad on eyes). Now issue is that working side of screen is HOT, like so hot that you cant hold hand on back of screen panel(aluminum housing). Are leds supposed to be hot like this? It is getting 135VDC into that side of led strip and led strip had single side of leds had 100 leds on it-per google searches. Not sure how it work but it works on only half of voltage to leds (you guys discussed replacing individual leds and they are 3.3veach)but it is HOT like to point that i think it would melt screen in next 30 minutes.
Each led strip has its own wires that go into 4 separate connector pins on Power supply and now I am using only one + lead and getting - negative from tvs chasis because power supply is not outputting - and if i connecti it that way it should be i get endles red blinking light. they way i got it hooked up everything works perfect(one side leds only) but its too hot.

Any suggestions? Thank You for your reply.




Samsung UN55D6000SF

[budm]

Re: Bad led strip Samsung UN55D6000SF

Soon that LED strip will burn up, I think you had bypassed the LED current regulator circuit for the LED by connecting one end of the LED string to Ground, the current return path of LED string is through PWM Controlled Power MOSFET and the current sensing resistor to maintain constant current flowing through the LEDs. That LED power supply should have gone into protection shutdown. I wonder how much current is flowing through the LEDs right now, you may see nice smoke coming out soon.
This is your board, right?
http://www.shopjimmy.com/samsung-bn4...ply-board.htm#
Samsung BN44-00424A (PD55A1_BHS) Power Supply / LED Board

[gavric]

Re: Bad led strip Samsung UN55D6000SF

Thanks for quick reply,
Yes that is power supply in this tv. Yes tv was disabled with red light blinking and nothing would help it and without leds connected tv turns on but no back light, can see images with flashlight. Anyway to lower that current by connecting that negative elswhere on this PS. I get 135VDC at red + point at diode-currently using that point because from pin1 at led connector i get 230VDC (and sometimes 430VDC???). Blue points(negatives) are dead and not doing anything besides disabling tv when i connect them to leds strips or single led strip.

Any way to lower current going into single side led strip or fool PS into powering strip without disabling tv(protection mode) and make it work as it is supposed to(turn completely ON/OFF via remote, etc) ? Blue potentiometer did not do anything to adjust/lower voltages.

[budm]

Re: Bad led strip Samsung UN55D6000SF

Right now we do not know the exact QTY of the working LEDs.
Can we see the pictures of the board with the LED connector in place and exactly how you have the wire connected to ground?
You may be able to use the resistor to limit the current to a safe level.
So far it looks like the LED strings are connected in series to form one large string, but I need to see the pictures to verify.

[budm]

Re: Bad led strip Samsung UN55D6000SF

You may be able to put dummy load in place of the LED strip that has open circuit.
See how the LEDs strings (two) are connected together. I will not run the TV right now until you are able to make the modification other wise you will brunt out the working LED strip which I am surprised it did not burn up yet.

[CapLeaker]

Re: Bad led strip Samsung UN55D6000SF

Soon that LED strip will burn up, I think you had bypassed the LED current regulator circuit for the LED by connecting one end of the LED string to Ground, the current return path of LED string is through PWM Controlled Power MOSFET and the current sensing resistor to maintain constant current flowing through the LEDs. That LED power supply should have gone into protection shutdown. I wonder how much current is flowing through the LEDs right now, you may see nice smoke coming out soon.
This is your board, right?
http://www.shopjimmy.com/samsung-bn4...ply-board.htm#
Samsung BN44-00424A (PD55A1_BHS) Power Supply / LED Board

x 2

that was not a good idea.

[gavric]

Re: Bad led strip Samsung UN55D6000SF

On the tv where led power wires wires go into screen it looks like they are branching of directly to left and right and they are not connected. I have working strip connected as in the picture bellow and it lights up one side only. if i try other side its not doing anything and measures dead, no resistance or changes anything on meter where i measure it in either diode mode or ohm mode.

I really dont want to open this screen up and try to replace 8 dead leds or chase new strips or something like that because i know it will get messy and I might mess the glass up at the very end. It would be ok with me if i could just "lower" current so it does not melt everything and leave everything as is(tv works nice with half back light) but i left it on for several minutes only.

[gavric]

Re: Bad led strip Samsung UN55D6000SF

I just got around to measure current going into led working led string. When multimeter is in Amps-DC mode- red multimeter probe on + wire going into led string and black probe on +135VDC spot on that diode (negative-black wire from string=chassis ground) on PS it measures 0.49.
When i flip it to Amps-AC it measures 5.03. not sure if Amps-AC mode matters anyways since we working with DC current.

[CapLeaker]

Re: Bad led strip Samsung UN55D6000SF

What are you trying to do? A bad LED string is a bad LED string. Since you have bypassed the protection on that bad LED string, I wouldn't be trusting it anymore.
In order to set things half ways straight, you have to open the panel and replace the bad LED(s). If there is only one LED bad, you could put a zener diode in it's place. The current is set by the LED controller for the whole string. I don't recommend bypassing / tampering with the protection circuits for permanent basis, regardless the excuse.