No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

[Chillin014]

Hello all and thanks in advance for helping me with this.

I am a novice TV repair hobbyist and just picked up this Samsung UN65MU6290 / PS board # BN44-00873C with no backlight but otherwise seemingly fully functional. My initial assumption was the LED strips were bad but upon further research apparently the Power Supply board can also be at fault for "over driving" the LED strips. On ShopJimmy they are recommending to replace some resistors and other components (transistors?) in conjunction with the LED strips (although their referenced Youtube link only demonstrates replacing the resistors):

"--PLEASE NOTE: This repair is recommended only for experienced technicians. After installing these LED bars, we strongly encourage you to perform the modification on the power supply board in your TV (BN44-00873C) that can be seen here: https://youtu.be/R_KuCkW1SO4
Replace resistors R9111 & R9211 as shown in the video with the included resistors from ShopJimmy.
After this modification is done, the LED bars will run much cooler than the stock ones and will prolong their lifespan significantly."

What has me especially paranoid is a comment I read from an eBay listing:

“On this model most of time one led strip and power board fail at the same time, to fix this issue you must replace that failed led strip plus power board. If you install this LED strip with failed power board and turn the TV on, LED strip will fail on the spot, also if you install a good power board with bad LED strips the same thing would happen to that power board. “

Is there any truth to this? How could bad LED strips ruin the power supply board?

I can solder but have not yet performed component replacement on a circuit board so I'm trying to approach this cautiously. I need some expert help to guide me through this logically. I'd like to test the PS board to rule it out as the issue before doing further disassembly to the TV to replace the strips.

I really appreciate any advice on diagnosing and fixing this.

[neilc6]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

I got one of these before and didn't even want to touch it. There are two different suffixes to the model number and one is edge lit and the other isn't. Extremely difficult to replace the strips if edge lit plus a screwless back cover. Samsungs typically don't have protection shutdown of the LED driver circuit and bad LEDs may damage the controller IC. I have experienced this on two Toshiba models.

[Chillin014]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

I got one of these before and didn't even want to touch it. There are two different suffixes to the model number and one is edge lit and the other isn't. Extremely difficult to replace the strips if edge lit plus a screwless back cover. Samsungs typically don't have protection shutdown of the LED driver circuit and bad LEDs may damage the controller IC. I have experienced this on two Toshiba models.

The screwless cover was a new one for me as well. Almost impossible to remove without cracking it in some way. I have once replaced some LEDS in an edge lit HISENSE and it was a pain but not impossible.

Anyway, I couldn't get any of the LED strips to power up using my tester at the harness but I'm not really sure I was making all the correct connections either.

I guess I should have posted the board # in the initial post if I expect any diagnostic help ( BN44-00873C)

[brucetv]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

Everything is true. Due to Samsung's incompetent engineers this model does have this fault. The led's on the 6290V are being overdriven and when one of these edge lit led shorts out it will damage the switching transistors at Q9101C and Q6201C and usually take out IC9101 with it. If you have a backlight problem you either have to buy both the power supply and new strip kit and change both at the same time or you have to repair the power supply and replace both strips. Don't get cheap or lazy or you will learn the hard way with failure of the new leds due to a faulty power supply or vice versa. If your a newbie I DO NOT recommend doing the backlight repair because this model is a pain in the ass to do and you will need good soldering skills to replace IC9101 on the power supply. Get a quote from a repair shop and let them deal with this headache POS. Here are pictures of this BL repair and the burnt bezel that holds the led strip.

[Chillin014]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

Everything is true. Due to Samsung's incompetent engineers this model does have this fault. The led's on the 6290V are being overdriven and when one of these edge lit led shorts out it will damage the switching transistors at Q9101C and Q6201C and usually take out IC9101 with it. If you have a backlight problem you either have to buy both the power supply and new strip kit and change both at the same time or you have to repair the power supply and replace both strips. Don't get cheap or lazy or you will learn the hard way with failure of the new leds due to a faulty power supply or vice versa. If your a newbie I DO NOT recommend doing the backlight repair because this model is a pain in the ass to do and you will need good soldering skills to replace IC9101 on the power supply. Get a quote from a repair shop and let them deal with this headache POS. Here are pictures of this BL repair and the burnt bezel that holds the led strip.

Thanks for the info! Jeeze this sounds like a tough one. I'm a newbie in the sense that I've primarily only performed LED strip swaps/ board swaps. I've done other soldering but not on a circuit board before. I found IC9101 but I couldn't find the other transistors you mentioned. How can I test if these were damaged (while in circuit preferably)? I'm up for a challenge.

CNL802 is the connector/plug for the LED and I can't make sense of the listed voltages in the diagram. I get about 317 volts on terminals 1, 2, 3 and 4. Terminals 5 and 6 which I believe are supposed to be ground I do not get a continuity reading. Terminal 7 I get minimal voltage: 0.12V and Terminal 8 : 0.02V.

[Chillin014]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

Some photos of the board

[R_J]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

The two transistors are mounted on the trace side of the board, the two resistors are likely R9111 & R9211 and it looks like shopjimmy replaces them with 4.7Ω

[brucetv]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

If you get the strip kit from shopjimmy also get the repair kit for the power supply. You will get the IC9101, the two switching transistors Q9101C and Q6201C, and the two resistors R9111 and R9211. Change them all. Do the repair first on the power supply and then replace the led's. It's such a pain in the ass to do the backlight repair on this model we turn them down now. I don't have time for this nonsense. Samsung you suck.

[Chillin014]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

The two transistors are mounted on the trace side of the board, the two resistors are likely R9111 & R9211 and it looks like shopjimmy replaces them with 4.7Ω

If you get the strip kit from shopjimmy also get the repair kit for the power supply. You will get the IC9101, the two switching transistors Q9101C and Q6201C, and the two resistors R9111 and R9211. Change them all. Do the repair first on the power supply and then replace the led's. It's such a pain in the ass to do the backlight repair on this model we turn them down now. I don't have time for this nonsense. Samsung you suck.

Thanks for the reply. SJ sells the kit but only has a video showing, and only makes mention of, replacement of the resistors. I'd like to test the transistors which would prove too risky for a novice to replace and see if I can "get away with" leaving them in place.

I lost my patience and disassembled the TV down to the LED strips, sure enough many of them were burnt. Some were essentially charred. I went ahead and ordered new strips from China so now I have about a month to figure out how I'm going to upgrade the board. Disassembly was about 5 steps more complicated than other TV's I've taken apart. Lot's of plastic snap points that likely won't withstand another disassembly.

[Chillin014]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

Hello all. It took me this long to get my replacement strips from China. I have installed them (and possibly damaged them during installation due to complications with the plastic retaining trim that holds the strips and aligns the large clear plastic panel).

Anyway, I'm still torn on what to do with the PS board. I feel comfortable replacing the resistors but not so much the other components in the shop jimmy kit :

And if the resistors are the main culprit I don't want to pay $20 for 10 cents worth of resistors.

Not sure how to approach this and whether it's safe to experiment with resistors first or what.

[nomoresonys]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

Check some youtube videos if you find the right one it will walk you thru it, you already did the hardest part, getting the back cover off. : just practice your soldering on a scrap board til you think your ready.

[Chillin014]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

Check some youtube videos if you find the right one it will walk you thru it, you already did the hardest part, getting the back cover off. : just practice your soldering on a scrap board til you think your ready.

Hahaha, and I really don't want to put that back cover on again until I know for sure this thing is fixed.

I've been watching some videos on YouTube but I really have no concept of what I'm replacing and why. I understand a resistor reduces the voltage to the LED's but going from a 1.7Ohms resistor to a 4.7Ohms resistor-is that okay? Is that safe or is it going to create a lot of heat?

And as far as the other components...I'd like to know if they are even defective before messing with them. I'm flying blind here

[nomoresonys]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

I believe the idea of using those bigger ohm resistors is to lower the current because a lot of manufacturers have way to much flowing and that's why the backlights fail prematurely, only reason I can think of WHY they do it is to break the tv in hopes that you will buy another from them. Can't see their logic tho, cuz the last thing I would do is buy a tv from the same company that planned my tv to break 2 months out of warranty.

[Chillin014]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

I believe the idea of using those bigger ohm resistors is to lower the current because a lot of manufacturers have way to much flowing and that's why the backlights fail prematurely, only reason I can think of WHY they do it is to break the tv in hopes that you will buy another from them. Can't see their logic tho, cuz the last thing I would do is buy a tv from the same company that planned my tv to break 2 months out of warranty.

Totally agree. But I'm wondering why the backlight brightness couldn't just be turned down in the settings to accomplish the same thing?

I'm waiting on my repair kit to come in the mail but I got impatient last night and decided to take the risk and power on the TV with the new LED's installed. They lit up right away and then dimmed and I heard some buzzing and freaked out and and unplugged the TV. This was all within less than 1 second's time. I thought maybe I fried the new LEDs so I used my LED tester to power them from the harness and they seemed to turn on but couldn't tell if the entire strip was lighting up.

Will await the repair kit and replace as much on the board as I can and try again.

[nomoresonys]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

A lot of times you can turn the backlights down in the menu even in the service menu, on a couple of my older tvs, not sure about the newest, I'll have the settings turned down and when I check them periodically, they have managed to jump up to 100 percent (vivid) again, with the pretty simple resistor mod, you don't have to worry if it has jumped up to the danger zone. They have been doing it for quite a while now, there's some on youtube.

[Chillin014]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

Well I sure appreciate the reassurance. After receiving my kit yesterday and seeing how tiny the transistors,etc are...I'm most likely going to put those on the back burner and hope for the best.

I have also confirmed the resistors I received, (which are also tiny compared to the ones I'm replacing), are 4.7Ohms resistors. I'm removing 1.7Ohms resistors. I will put my faith in the circuitboard gods and proceed.

[Chillin014]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

Update : I replaced the resistors, no problem. All went smoothly in that regard. I plugged everything back in and the LEDs immediately began buzzing again. I decided to wait a moment longer and the LEDs continuously flashed on and off with a lot of buzzing. I actually think the buzzing might be one of the LED's arcing as I could see light shining through the holes in the back casing and in one particular area there was a more yellow colored light that seemed to flicker in sync with the buzzing.

This would re-affirm my concern about damaging the LED during installation. I guess I'll be taking it all apart again and maybe I can salvage an LED from my old strip and rework it.

[budm]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

Just curious, what is the designator for the 1.7 Ohms resistor?

[Chillin014]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

Just curious, what is the designator for the 1.7 Ohms resistor?

I don't understand the question. The original resistor colors were Brown, Violet, Black, Silver, Brown. That's about all I know about them. The body color was that seafoam green color and they were at least twice the size of the new ones.

[budm]

Re: No back light on Samsung UN65MU6290, Need help modifying Power Supply Board.

Part designator: Example
R1 means the desigantor of that particular resistor is assigned as R1, so that 1.7 Ohms resistor must have designator so you can put in the correct resistor at the correct location.