Samsung UN75F6300AF help

[jxgx]

Ny Samsung UN75F6300AF was dark and shaded on the upper third. I replaced all of the LED strips. The old ones were copper backed and some had visible burned components on the strips. ( diodes or resistors?) The new one fit perfectly and are aluminum backed.
I reassembled it and it's clicking on and off, I unplugged it overnight and tried again. Same result
If I take the screws out of the power board, bn44-00621c, and move it off it's grounding points and unplug the mother board the lights will come on and stay on. If I move it back into position where the corners of the board contact the aluminum backing or plug the mother board back in, it reverts to the clicking on and off. I assume plugging in the other board also grounds the power supply through the harness.
Nothing looks burned on any connections or the board and no caps look expanded.
Any thoughts? Thanks!

[Storyteller12]

Re: Samsung UN75F6300AF help

If it worked before you took it apart then must be something you did while putting back together that’s shorting the power board. Double check all your connections etc.

[Devil_rider]

Re: Samsung UN75F6300AF help

Check connections to led strips . You might have pinched a cable that goes to ground now or strips are bad and have a connection to ground.unplug them from psu and ohm the wires to ground, they should be open circuit.

[Biruslapio]

Re: Samsung UN75F6300AF help

Does this TV has that evil way of fixing the LEDs to the screen?

It is the metal clips way, you slide the LED boards into them, and they get scratched, short to ground and die immediately, I paid top money for a UN55F6200 LED kit, only for 10 of the strips to die due to this hateful way that samsung chose to do it, it is made to ruin maintenance.

The LEDs shorted and died because they leaked a lot of current directly ground somewhere in the boards. I used a plier and pulled back all those clips embedded in the chassi. Had to mix/match with the older set that was not too good, since warranty was not a thing anymore (boards were clearly scratched).

[jxgx]

Re: Samsung UN75F6300AF help

Thank you so much for the above 3 responses. All correct and helpful. I was trying to not take that part of the tv back apert. One row is shorted to ground. It not the install like I was fearing, the 1/3 piece of my 3 piece row is faulty. It’s the piece furthest from where the row plugs in. The piece out and just laying on the chassis shorts to ground. I’m wishing I had the old ones but I don’t. I now need to find a replacement strip. Would the tv function without it? I’m thinking of making that the bottom row so only a corner would be a bit dim until the part comes.

[Biruslapio]

Re: Samsung UN75F6300AF help

It's just better to wait for a replacement.

[jxgx]

Re: Samsung UN75F6300AF help

I realize that but waiting for Amazon to work it out with the Chinese vendor might take a while. Would it work? Would it harm anything? My gf would like the dining room table back.

[Biruslapio]

Re: Samsung UN75F6300AF help

Calculate how many leds, their voltage and power ratings, then wire up a resistor in series that equals the load of the missing led strips. Not recommended.

[jxgx]

Re: Samsung UN75F6300AF help

An interesting thing happened during testing. Even though the tv had been inplugged and apart for 24 hours, when I was testing near the end of the bad strip, connecting the meter between the chassis and the strip made the led next to it light up. Not brightly but clearly liti did it a few times to be sure. Much is written about caps holding charge but it surprised me. It didn’t happen anywhere else on the strip.

[jxgx]

Re: Samsung UN75F6300AF help

Thanks for the resistor response.I think waiting for the part is the way to go then. That’s more than I want to deal with. The connectors are fragile and I’d want to be able to just snap the replacement in with no issues.

[jxgx]

Re: Samsung UN75F6300AF help

Ok, parts came. Put them in. No shorts to ground anywhere between led strips and aluminum backing of the tv. I bought a light strip tester and each strip lights up with the same voltage displayed. I checked them from the strip they all connect to one at a time. I have the same issue. If the power board is loose and insulated from the backing, and unplugged from the other boards, all the lights come on and stay on. If I install the board or plug in the other boards, it goes right into the snap on and off mode. Any ideas? Thanks!

[Storyteller12]

Re: Samsung UN75F6300AF help

So, all lights work when the mainboard is unplugged from the power supply correct?

And if you plug-in the mainboard 1 row is out? It’s the same exact row as before?

Does the tv power on and work even with the 1 row out?

[jxgx]

Re: Samsung UN75F6300AF help

Yes, it was also unplugged from the light strips when I tested the lights.
No, it goes into clicking on and off if I plug in the main board or install the power board to the aluminum base the lights attach to

[howardc64]

Re: Samsung UN75F6300AF help

Need to check for continuity of backlight wiring against the chassis. Installing PSU will turn chassis into PSU ground.

I've experienced the following

- 1 bad light strip shorting + to back of strip which then grounds against PSU. Presumably not your problem with new strips

- pinched + backlight wire under the mounting block for the feet/stands.

Don't know what you mean by "snap" on and off mode and "clicking" on and off. Is the TV turning on/off by itself and you hear some clicking sounds?

[jxgx]

Re: Samsung UN75F6300AF help

Yes, on/off click each time
I did have one bad section in one row on the new strips. It’s been replaced now. I’ve checked everywhere I can think of with a vom set to ohms and an audible sound. With the power supply out, I can’t find any short.
I’ll try again with the power supply in. Are you referring to where the strips plug into the tv backing plate to check for pinched connections?

[howardc64]

Re: Samsung UN75F6300AF help

Yes, on/off click each time
I did have one bad section in one row on the new strips. It’s been replaced now. I’ve checked everywhere I can think of with a vom set to ohms and an audible sound. With the power supply out, I can’t find any short.
I’ll try again with the power supply in. Are you referring to where the strips plug into the tv backing plate to check for pinched connections?

Is this your TV's LED strip layout?

https://www.youtube.com/watch?v=KvI7...nnel=ShopJimmy

That vertical bar which all the LEDs connects to might be where the short is. Looks like new LED strips don't come with that bar.

This video shows your TV"s LED power distribution isn't through the typical wires. It is routed through that vertical bar. Looks like PSU connects to the bar in 2 places. The bar then distribute power to all the rows. Sounds like there are parallel LED power routing channels in the vertical bar If you had top 1/3 LEDs out. So at least 2 and maybe 3 circuits. Anyway, possible short in the vertical LED power distribution bar.

[jxgx]

Re: Samsung UN75F6300AF help

Yes.
You are correct , they don’t. I’ve tried to check it for that at each connection point and didn’t find anything. Maybe I need to take the strips out and look.

[howardc64]

Re: Samsung UN75F6300AF help

Yes.
You are correct , they don’t. I’ve tried to check it for that at each connection point and didn’t find anything. Maybe I need to take the strips out and look.

With LED installed but before assembling LCD panel and PSU. Check every + line on every LED strips against the following

every - line on the PSU connector on that vertical bar. I'm guessing you've tested this.

against the chassis! If a + line on that vertical distribution bar is shorted to the back of the bar but not shorted to the - where PSU is connected to the bar. Then you won't see the short until PSU is connected to the bar AND grounded to the chassis to complete the short circuit. This is likely exactly where your short is. If so, then solution is 1) get a bar that don't have internal short against its backside 2) insulate back of the distribution bar agains the chassis. I did this once (on an LED bar that shorted to its backside which touches chassis) but often end up chasing and insulating everywhere the short went. In your case, the LED vertical bar is also connected to all the strips and all the strips have their backside grounded to the chassis as well.

Think of it like this... thin bar that distributes multiple + - current in layers above a metal bar that is the heat sink with thin insulator between all. If a component blew up with enough heat, it can easily breach the insulation. For example + to the heatsink. Which won't show up as short until PSU complete the short circuit against the chassis.

[Storyteller12]

Re: Samsung UN75F6300AF help

Did you put the black plastic sheet back under the power supply? Sometimes you have to remove it to get the stand-off clips off that hold the diffuser and screen up in the middle. Make sure you put that back if not.

Do the lights come on with power supply installed and mainboard unplugged? You said yea above but I think that was with power supply not screwed into the chassis

[Biruslapio]

Re: Samsung UN75F6300AF help

I do not think it is the black sheet since they said the leds just stop working even if mainboard is plugged, one or more led bars are shorted to ground like I said in my first message here.

This tv has those metal clamps that scratch the pcb and short the bars to ground, usually killing some LEDs in the process, samsung had to have done this on purpose to kill repair attempts.

Unlink the bars from the PSU and use your multimeter in MegaOHM scale, if there is any resistance between + or - led to chassi = something is shorting, then you start removing one by one until you find it.