[SOLVED] Repair of Samsung 55" TV - backlight problem

Friends of mine have a Samsung 55" 4K TV, model UN55HU6840 (about 2014). They say they can hear audio, but the screen is black. I'd like to take a shot at fixing it for them since they don't really have the money to buy a new one. The encouraging thing is that until recently this has been an intermittent problem that's just gradually gotten worse, and now is permanent. But I'm encouraged to think it's not burned out LEDs, else it would never have been intermittent.

I just told you everything I know about repairing TVs, but am generally experienced in electronics as a hobbyist. Based on some Youtube videos it seems I should take off the back cover and check all the connections. Then I would go to the power board and check the voltages on the lines going to the backlight LEDs, and if low, start checking diodes and electrolytics, and of course look for bad solder joints.

Does this sound like a reasonable approach? Is there a typical cause of this symptom?

I've had no luck finding a schematic. Does anyone know where I would find that?

Well, any guidance would be appreciated.

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Have your friend turn on the TV and pretend that it has video. Make sure he can hear the audio that goes with the video. Have him take a flashlight and illuminate an area where you know there should be a picture. No movies with dark scenes please. Have him move the flashlight around and try different angles and room lighting. If he sees anything that looks like a faint image on the screen, then the TV has an backlighting problem. That model uses LED edge lighting, so look for problems in that area. If he doesn't see anything with the flashlight, then it's a video problem. Your approach is ok, but without a service manual and a schematic, repairing a PCB might be problematic. Think about isolating the problem to a particular PCB and order a used replacement from the cannibals on eBay.

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Jeff Liebermann

They've already taken it down and put it in the garage, so I'll have to do the flashlight test when they bring it to me. But I have a little more information.

This happened before, about three years ago, and they spent $250 at a local repair shop, which replaced one of the boards. But they don't know which board, and don't have the paperwork that might tell. But they say the symptoms are the same.

I found a repair video of this exact model:

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which turned out to be bad electrolytics. I haven't done a lot of repairs, but so far pretty much all of them have been bad caps - usually high ESR. Most recently, that's two Disney coffee mug warmers and the power supply for my Ooma box. Anyway, what I'm hoping for is either a bad connection, or a bad solder joint, or some component on the power board that I can replace. I'm encouraged by the size of the components on that board - not all tiny 0201 smd, but through-hole stuff as God intended.

Well, I'm not sure anything will come of this, but I think it's worth giving it a shot. And working on stuff like this is my idea of a good time. But I would sure like to find the schematic

Film at 11.

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You might be able to identify which PCB was replaced by inspecting the heads on the PCB mounting screws for wear caused by the screwdriver bit.

I don't know about your local repair shop. The lack of historical information sounds like they want you to bring the TV in for another repair instead of fixing it yourself.

In California, repair shops are required to keep records for 3 years.

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9842. One copy shall be given to the customer and one copy shall be retained by the service dealer for a period of at least three years.

2764. Record Keeping - Customer-related Records A legible original or legible copy of the following records shall be retained by the service dealer for a period of at least three years: invoice, customer claim check, estimate records, and employee records.

If your friend paid sales tax on the parts, the shop has to keep records for 4 years.

Different states will have different rules and time periods.

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Jeff Liebermann

The HU series *does* have intermittent issues with LEDs, either from individual LEDs or the interconnects on the strips. Sometimes you can change just the bad LEDs or hardwire the interconnects if there is a voltage drop across them, but the best option is to order the complete set of strips from someone like ShopJimmy.

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You might try a manual 'reset to factory', or a USB re-flash. These procedures don't need an active screen or remote.

I've yet to run across an audio-ok/blackscreen situation, so can't advise.

You can take off the back and hunt for obvious problems like bulging caps or iffy connectors.

To troubleshoot, you'll really need to get a service manual. This should tell you how to get the back off, without bending something. It will also offer test points for measurement.


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I looked at the user manual and searched the internet for such a procedure. There are two resets. One for resetting the smart hub and another for resetting everything except the network settings. Both are access from the setting menu which requires seeing something on the screen. There are probably instruction for a factory reset without using the remote or screen, but I couldn't find them.

Running across or otherwise trampling the TV is not advisable.

Not all electrolytic capacitor problems are easily recognizable as bulging or leakage. I suggest an ESR tester to be certain.

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Jeff Liebermann

Having no experience with these TVs, I don't know how the LEDs are connected to power lines, or how the lines are interconnected. Because of the level of disassembly needed to deal with LEDs, I'm hoping that it's a power board issue.

I looked around at ShopJimmy, and they are out of stock of most things. I don't know what might be available on Ebay.

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Try here with this link:

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Click on the Manuals and downloads link on the menu selection you can choose from.

watch for the hot spots on the invertor board. When working with IC's, where a ground strip.

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Charles Lucas

The HU series uses LED strips which plug into a single strip running at a right angle to the rest at one side of the array. Most back-lit TVs just use a plug in wire connector for each strip, but Samsung did away with most wiring on this model. The power supply board LED output connector plugs into chassis mounted connector which is hard wired to the single mounting strip that the rest of the strips connect to inside the display. There is no wiring on this version except PC wiring. I've had both bad LEDs and bad interconnects on the HU, which is why I recommend total replacement of the strips inside the display.

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ShopJimmy shows stock on set of LEDs for this model as I type this. They probably have more on order.

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You're right. It looks like only Panasonoc, Sanyo and Sony sets have a side-button power-on reset.

For Samsung audio/no image symptoms, the 'troubleshooting tree' branches out as

-check LVDS connector

-change tcon

-change main board

Not very helpful. Unlikely it's a power supply issue, but bulging caps are common, even so, on sets of this era.

Some TVs are too smart for their own good.

Haven't had one for personal use since 1978. Bloody waste of time.


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Some sets have a power-on keypress sequence that invokes a 'Factory Mode', which can be unproductive, if not downright destructive, if the screen isn't visible. Remote botton functions may not as labelled.

So unless the manual says it, don't do it.


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From an old web search:

Factory Resets Listing Over time, I have created a listing of manufacturers and their factory reset/factory mode procedures that may help others. This list is from my own experience, and is by no means complete for any given manufacturer. Some have been found by searching the internet, some by trial and error. I hope some may find this information useful

**** WARNING!!!! ******

Some of these procedures may allow you to enter factory service modes. IF YOU DO NOT KNOW WHAT YOU ARE DOING, DO NOT MAKE CHANGES TO SETTINGS IN FACTORY MODES!! Improper settings may cause undesired operation, and could result in a situation where your TV cannot boot/turn on.


Factory Resets / modes

For all listed procedures, start with TV on, in TV mode, unless otherwise instructed. After procedure is complete, unplug set and re-plug in to finish reset.

If more than one procedure is listed for a given manufacturer, try the different ones until you see which one works for your set.


Enter menu, hi-lite “audio” then enter 8893

mode/source 2580 select “other setting”,select “shipment” then yes, after it exits service menu you need to power set off.

Dynex ****************************************-

source/input 2580

hold vol down on tv and hold #1 button on remote, vol will jump to halfway and set shuts off. Turn back on have 1st time setup screen.

source/input 2580

menu 1999 (tv is on)

Element ****************************************

menu 0000

menu 1147

Haier ******************************************

pull up menu, hi-lite “audio” then enter 8893

Hisense *****************************************

In customer menu go to”Parental” enter 0000 then select”Clean All” then power the set off and back on and first time setup menu will be there.

For some models, same as above model except in menu it is labeled “Lock”

Insignia *****************************************-

input 2580 (tv is on)

Mitsubishi ****************************************

Menu 123 or menu 2470 (tv is on)


Hold vol- on TV, press and hold menu button on remote

Philips ******************************************

Push menu, select”Features”then select”current software info” push

062596-info on remote then push info again then red”initialize appears and changes color then complete. Push power button to exit

TV is on,push 062596-info on remote,then push info again, red”initialized”appears it turns green when completed, then push power button to exit

Polariod *****************************************-

Hold vol- and chan- or hold vol+ and chan+ (tv is on)

Proscan ******************************************

In customer menu go to setup,select parental control menu, enter 0000 then select “clear channel list”.

RCA *******************************************-

Menu 1147

Sanyo *******************************************

hold vol down on TV, press and hold #1 button on remote, vol will jump to halfway and set shuts off. Turn back on have 1st time setup screen.

Samsung *****************************************-

Mute 182 power (tv is off) (On some models, Factory Reset is on this menu, on some, you must go into the “Options” submenu

Seiki ********************************************-

Menu 0000

Sharp ******************************************** (Note – On Sharp models, you will need to look through the menus to find the reset option)

menu 1999

menu, 3481

menu 1147

while holding vol– & input buttons on tv plug in set when “k” appears push vol– & chan-

Sony *********************************************

Hold “arrow up” on remote and push power button on tv (tv is on)

Symphony *****************************************-

Source/input 2580

Toshiba ******************************************-

on Menu, select “Installation”, then “System Information” press the right arrow button, (“System Information” will change to “Factory Reset” or something similar) follow on-screen instructions

Vision Quest ***************************************- Source/input 2580

Vizio ********************************************

In customer menu under “Help” tab is Factory Default enter 0000


Vestel (most): Menu 4725 then select "RESET"

Samsung (European): Power off, Info - Menu - Mute - Power, then find factory reset and execute option.

LG/Zenith: Hold MENU on TV and MENU on remote for 5~10 seconds, then select reset option.

NEC: While powering on hold "MENU" or "INPUT" on TV, depending on model. (Only disables error lock out/buffer and puts TV in temporary service mode.) To reset to factory, on remote, Off Timer - Menu - Exit - Off Timer, then select reset option.


Vizio Service Menu Method 1

  1. Turn The TV off.
  2. Press and hold the {CH +} & {CH -} buttons on the TV.
  3. Then press and release the {POWER} button on the TV.
  4. Release the {CH +} & {CH -} buttons.
  5. Now press the {MENU} button on the remote.
  6. You should get your regular menu up, but with a "F" in the bottom right corner of the menu (This is for factory).
  7. Press and hold the {MENU} button for few seconds.
  8. The Service Menu will be displayed. Vizio Service Menu Method 2
  9. Turn The TV off.
  10. Press and hold the {CH +} & {CH -} buttons on the TV.
  11. Then press and hold the {POWER} button on the TV.
  12. Keep all three buttons pressed for few seconds.
  13. Now press the {MENU} button on the remote.
  14. You should get your regular menu up, but with a "F" in the bottom right corner of the menu (This is for factory).
  15. Press and hold the {MENU} button for few seconds.
  16. The Service Menu will be displayed. Vizio Service Menu Method 3
  17. Press and hold the {EXIT} button on the remote for 3 seconds then release it.
  18. Then press the {1} {2} {3} buttons on the remote.
  19. To exit, press the {EXIT} button.

--------------------------------------------------------------- GV42L FHDTV10A / JV50 / SV42 / SV320XVT / SV370XVT / SV420M / SV470M / SV420XVT1A / SV470XVT1A / VECO320L1A / VO22L / VO32 / VO37 / VO47L / VOJ320 / VOJ370 / VP322 / VP42 HDTV20A / VP422 / VS420LF1A / VU42 / VW32 / VW37 / VW42 / VX20 / VX32 / VX37 HDTV10A /VX42

Push "Menu" on remote and then push "Vol-" and "Input" on keypad

GV46 / P50HDM / P50HDTV10A

Press "Ch-" and "Ch+" buttons together once on keypad

GV42 / L42 / VP42HDTV10A / VP50 / VX37

Press and release "Menu" on keypad. Hold "Ch-" and "Ch+" buttons on keypad, then hold "Menu" on remote.


Hold "Ch+" and "Ch-" along with "Power" on keypad. OSD will show "F" on right bottom portion of OSD.


Press "Info" on remote, then press "Right Arrow," "Down Arrow," "Left Arrow," "Up Arrow," "Right Arrow." The TV will show "Enter Factory Mode." Press "Menu" after message disappears and go do to "Setup."


Press "Menu" then press the following combination: "Info," "8," "2," "0," "6."

SV420M / SV470M / VF550M / VF550XVT1A / VF551XVT / VL260M / VL320M / VL420M / VL470M / VO320E / VO320EP8 / VO370M / VO420E / VP504 / VP505

Press "Menu," and then press "2," "4," "8," "9."

SV420M / SV470M / VF550M / VF550XVT1A / VF551XVT / VL260M / VL320M / VL420M / VL470M / VO320E / VO320EP8 / VO370M / VO420E / VP504 / VP505

Press "Menu," and then press "2," "4," "8," "9."

VA19 / VA22LF / VA220E / VA26

Press "Menu" and then press the following combination: "0," "6," "2," "5," "9," "6"

VA320E / VA320M / VA370M / VT420M / VT470M

Press "Menu" and then press the following combination: "1," "9," "9," "1"

VW22 / VS370E

Press "Mute" once OR "-" twice (the dash next to the "0") and then press the following combination: "9," "8," "7," "6"


PANASONIC lcd and plasma TV's service menu (factory reset is done via menu)

press and hold volume down (on tv panel) while still holding vol- press i (info botton) on remote three times

service menu starts up - scrolling pages is done by color botton (green if not mistaking

*usefull for people who know what they are doing (not me at the moment)

-i found it usfull only for white wash for plasma TV's (just scroll throuh the menu untill you see the white wash apears

exit the menu by turning off the TV


Here in South Africa - and I guess most of the Southern Hemisphere - we are reluctantly getting used to a myriad of Chinese sets with Anglic-sounding names like 'Ultravision' and Germanic ones like 'Bauer'.

Inside they are mostly Chinese generic boards and most respond to the following for factory mode:

Hold down volume minus (Volume down) on set and press 'recall' on remote. 'Recall' is the button that activates the channel number and clock onscreen. After you have made your changes, in most cases, pressing 'power' on the remote will clear the factory mode.

On some models pressing the 'AV' button will revert things to normal operation. In rare cases, the sequence first described above - (Vol - on set and recall on remote) will have to be repeated at least once more.

If none of the above methods works, try using a universal remote - best one that has a LOT of in-built models..!

Search through the available models looking for any that suddenly causes the set to change channels.

Lock this setting into the remote and press '2'. Factory mode should appear.

BE WARNED that NONE of the remote's buttons will function normally!

Use the front panel buttons to scroll through available menus and make any changes. Power off set to revert to normal functioning.


Lamp Error Reset for Sharp LCD TV.

With power LED off (TV in fake standby or AC power plug removed) hold Vol- and SOURCE/INPUT.

Power on the TV. Do not release the buttons.

This may take up to 20 seconds.

Look for a letter "K" on the side of the screen when it powers up. If this appears, continue. If not, repeat the above procedure.

Press CH- and VOL- to access service menu. See if LAMP ERROR appears in listing. If so, then a reset procedure is necessary

Page through the menus looking for "L ERR RESET". Execute the option (highlight and press OK.)

Power off the TV (TV in fake standby or AC power plug removed)

Hold Vol- and SOURCE/INPUT.

Power on the TV. Do not release the buttons.

No "K" should appear.

Power off the TV.

The TV should now be fixed.


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Hisense TV..... goto menu, sound, balance set to "0" then press 1969 be carefull....

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Ok, this is the first hands-on update.

The TV arrived this morning. I hooked it up to my computer via HDMI (it was, of course, the last HDMI connector I tried) and I get audio. Running the flashlight test, I can see the icons on my desktop and any video I play on the computer. The screen is dark, but as I understand it, passing the flashlight test means the video is working, and it's the backlight that's out.

However, the owner brought his paperwork with him, and I found the invoice for the repair done in 2017. He says the symptoms were the same then as now. The invoice says they replaced the main board, #BN94-08076A. They charged $135 for the part.

I doubt I could repair the main board, but I think it's still worth taking a look. After all, I don't know that the invoice reflects what they actually did to fix it. And even if it was the main board last time, it could be something else this time.

Perhaps it will be obvious when I take the cover off, but it seems to me that one test would be to disconnnect the main board from the power board, and see if the LEDs light up. If they do, then it is the main board that's keeping the LEDs off. If they don't then it's either the power board or the LEDs. But is it possible to test what the voltage should be on the lines driving the LEDs? If the LEDs are in series, then it has to be high enough to drive all of them, so maybe 150V or more. Is that right? What I'm looking for is a way to test whether the power board is working or not. Well maybe the voltages will be printed on the board. In the videos it looks like they might be.

I'm just not clear how the LEDs are driven. Are they like the old Christmas tree lights - all in series, so if one burns out they all go dark? Or are they in parallel, or what?

Still no success finding a schematic or service manual.

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In *this* model, they're all in series and it's a one channel LED system - one LED or if one interconnect opens, no light.

Samsung doesn't publish schematics anymore. Just block diagrams and wiring diagrams at best.

An easy test on this model is to unplug the harness between the main board and the power supply and plug in the AC. With the main disconnected, the on/off line pull-up resistor will put the power supply into free-run, including the LED drive. If the back light comes on, the main *or* the power supply board is bad. If the LEDs come on, post that and I'll walk you through isolating the main or the power supply.

If the LEDs don't come on with the main disconnected and the AC applied which is what I'm confident you'll find, measure between BD9101 (either side) and J858 on the top side of the board near the LED harness. Should be more than 150V-300V (depending on whether this uses 3V or 6V LEDs) there between those jumpers. If it's there or higher, the problem is inside the display - either a bad LED or open interconnect between the LED strips.

No voltage or low voltage between those points? Bad power supply.

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Ok, so the main board controls the brightness of the LEDs through some kind of PWM signal to the power board. If so, then it seems to me if the LEDs fire up when the main board is disconnected, then the main board is the problem - something is grounding that signal line. It seems the power board has proved it's ok.

But it does occur to me that if nothing else on the main board is bad, then you could replace the PWM signal with something coming out of an Arduino. :-)

Yes, that makes sense. I don't have a lab power supply, but if I could borrow one, it seems another test would be to disconnect the LED strips and reconnect them to a power supply. You could ramp up the voltage to see if the LEDs light up at some point. If they do, then they aren't the problem. If they don't, something is open.

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Just use a voltmeter. DC's good enough for this lamp issue.


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On the ShopJimmy page for this model, it shows the LED package as seven strips of eight LEDs, plus seven strips of five LEDs. That's 91 LEDs. If they're all in series, then

3V LEDs would need 273V. So perhaps the strips are wired in some parallel configuration?

I'm starting on the diagnostics this morning with a neighbor who I discovered used to work for TI back in the day.

One of the ShopJimmy videos say flatly that if you pass the flashlight test, with audio, then a dark screen is either the power board or the LEDs. I guess that's not absolutely always true, but seems logical to me. I'm hoping for the power supply to be the problem. I'm not sure I would be willing to tackle the LEDs. I've watched those videos, and it's a major undertaking, with lots of opportunities to break things.

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Unlikely :(

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Adrian Caspersz

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