There are lots of reports on the reddit tvrepair subreddit of NU series TVs with failed backlights. NU is a 2018 model year and backlights are failing after 2 years. These models are edge lit from the bottom so LEDs that have burnt out will cause dark vertical bands or sections.
Some model numbers include
UN50NU6900F UN55NU6900F UN55NU6950F
With the screwless back cover and edge lit design, replacement can be pretty difficult especially on a large screen.
It is always recommended to never run your backlights at maximum which shortens their life.
Another reddit post shows that the LEDs can melt the clear plastic panel that spreads the light behind the panel.
Here is what edge lit LEDS look like behind the panel.
Model UN50H5203 UN50H5203AF UN50H5203AFXZC AH01 UN50H5203AFXZA
This TV had no power and didn’t turn on. The standby voltage was low indicating a damaged power supply. This model year does suffer from backlight failures and probing the connector to the LEDs indicated a lot of shorted ones. I suspected the bad backlights had damaged the power supply though the FET and diode for the LED driver tested good. With the LED connector unplugged, the standby voltage was normal again and the TV could power up. I confirmed the screen was good and I was getting video. I ordered replacement strips and a new power supply board since I suspected the LED controller was damaged.
Panel part number DF500BGA-B1 Power supply BN44-00772A LED strips (4 rows) LM41-00001Q LM41-00001Z 2013SVS50
Flickering and double images and horizontal lines are symptoms of a bad panel and typically not repairable. However there may be a workaround by blocking pins to the panel.
To determine if this workaround will work, first make sure your TV has a separate Tcon board. Newer TVs may have integrated Tcon boards so you will be out of luck in this case. Next, you will need to power up the TV with one side of the TV connected at a time to see if one side will display a good picture. With the TV unplugged, disconnect the ribbon from the tcon to the panel one side at a time. It is locked in place by a flip lock that will need to be lifted up to unlock.
If one side shows a good picture, you can try the technique in these youtube videos and block connections on the bad side. When inserting and removing the ribbon cable, it will be safer to UNPLUG the TV between attempts.
If the tape cutoff method doesn’t work, the very last resort is to look for side tabs on the bad side (if there) and rip them completely off.
Why Does This Work?
The panel is driven by drivers which drive both the left and right side and if one side has failed, blocking the connection to them will block the faulty drivers but the other side can maintain the picture. The analogy would be if one kidney was causing you pain so we remove it but you still have a second kidney.
How Long Does This Last
This workaround could last years or until the other side fails.
Update: Some new youtube videos from Frugalrepair about this fix
The Vizio M series has a common issue with the BGA connections on the main processor. Over time and repeated temperature cycling, the leadfree solder balls will crack and loose connection to the board. This problem is also found in Xboxes, PS3 and some laptops.
Diagnosing The Failure
Typically the TV will turn on but with no backlight. With the back cover removed, you should measure the 12V , PS_ON (pin 14) and ON/OFF (pin 15) pins with the ground on the chassis on CN9101. 12V should measure 19V and be stable. If it isn’t, the power supply also has a common failure. With the TV on, PS_ON should go logic high (> 2.5V) as well as the ON/OFF (BL_ON backlight ON) pin. ON/OFF not going high is a sign of failure.
With the TV unplugged, you can try heating the processor up with a hair dryer before plugging in. This test is equivalent to wrapping a game console or laptop in a blanket to get the processor hot and expand the solder ball joints enough to make contact to turn on.
Baking the board (or heat gun). There are a lot of guides for baking boards but I have found that results are temporary and only last weeks or months
Purchasing a new main board. Since this is a common failure, a brand new board may only last 3-5 years before this problem occurs. The processor on these models run very hot.
Reballing. If you search ebay, there should be repair services offered on ebay. Reballing will replace the solder balls with leaded ones which should last longer. Reballing is an expensive repair and should be over $100 USD and have a 1 year warranty. Beware of services that may just reheat the processor (lower price and short warranty).
This TV turned on but the backlights flickered and didn’t stay on and there was no video. I found out afterwards from the owner that the panel had been hit. Usually cracked screens still display video.
Unplugging the main cable from the power supply to force the backlights on showed a 2 inch crack on the edge of the screen. This model does not have a tcon board and the function are integrated into the panel which may have caused the no video situation. With nothing to lose, I ripped off the tab bond at the location of the crack and was able to get the TV to turn on and display video. The L shaped crack had also caused horizontal lines to emanate from that point.
This TV had no power and had the same power supply as an Emerson TV I repaired here. Board is marked BA3AT0F0102 2. The main fuse was not blown and the main switching FET was not shorted. Checking the diodes, I found D653 shorted (SB3A0, 100V, 3A). Replacing this part got the TV working.
However, I found that once the TV was turned off, it would not turn on again without unplugging the TV for a few minutes. The main board uses a processor associated with EEPROM failures in low end models. I wasn’t able to read the EEPROM part number but suspected it could be Winbond W25Q64B which is a common failure. I was able to read it and reprogram into another IC. Once installed, it fixed the turn on problem.
This TV had no front LED and no standby voltage. The main fuse was not blown but U807 was shorted. R818 also had visible damage and measured open so it acted as a fuse. U808 was marked CS8N65F (NCH, 650V, 8A) and is the main switching FET for the PFC circuit. I subbed it with a 450V part since 650V is overrated. R818 is 0.39 ohm 1W. With both replaced, the leg of C822 (100pf 1KV ceramic) burnt up when I plugged it in. There was also damage to N834. N834 is marked 1271A and is a PWM controller NCP1271 still available at Digikey. I have ordered both parts and a replacement board. Power supply is HLL-4255WJ.
I have encountered a similiar problem in Insignia model NS-48D510NA15 which uses a similar power supply design HLL-4855WC. I found the same FET shorted and the PFC only partially on. I suspected a bad N834 IC in this board as well.
This TV turns on and off but with no backlight. Sonys typically will flash a blink code but not in this model. Disconnecting the backlight connector has the same behaviour and no blink code. I was able to power on one out of the four banks of LEDs with my LED tester to confirm the TV had video when turned on. Each of the 4 banks read a little different with my LED tester with the expected voltage 6V x 29 LEDs = 174V
Panel number is LTY550HJ04. Research indicates the LJ64-03774A is the part number for the LED strips (SLED 2012SLS55 7030 58 R & L with 5 pin connector) . I have ordered the strips and will confirm the part once I receive it.
Update: Strips arrived and the old strips had lots of bad LEDs. During disassembly a small piece of tape floated onto the plastic diffuser and the glue residue caused a bright glow. I was able to remove it with acetone.
LG LN series TVs are very prone to LED backlight failure. See this post here. To reduce the chances of future failures, it is recommended to keep the backlight level between 50-60 (max 100). This step needs to be done for every input you are using. If you run a smart app, the backlight could be set back to 100 by default and it is a bit tricky to lower the backlight level.
Under Settings and Picture, picture modes Standard and Vivid both set the backlight level to 100. Eco mode is at default 70. For any of these modes, you can manually turn the backlight down. If a default is changed, the picture mode has a (User) suffix added indicating it has been changed from the default.
The Energy Savings feature will turn down the backlight level in in a dark room but will increase it in a bright room. It is better just to keep this setting OFF.
While we are in this menu option, motion smoothing is a feature which adds frames to make video smoother. While good for sports and other fast action scenes, it can make movies look like soap operas losing the cinematic effect. You can turn it off under Picture Options. Turn both Motion Eye Care and Trumotion OFF.
You need to perform the above steps for ALL inputs you are using since the settings are only applied to the currently selected input.
With apps, the settings option may not work. If it doesn’t, look for a button marked Q.Menu on the remote. Press this when a video is playing and it will bring up a different menu. Choose, Set Video. You can then turn the backlight down and turn off motion smoothing. You need to do this for every app you are using including the media player.
This TV turned on but with no backlight. Samsungs generally don’t shut off the backlight with failures so it was assumed there were open LEDs. Unplugging the cable between the main and power supply boards still had no backlight. With my LED tester on each of the 7 strips, I found open circuits in two of them. Moving good strips to the top rows, I was able to get half the backlight to light up and I reconnected the panel to confirm it was not damaged. This also confirmed the TV could start up and display video.
The LEDs have a footprint with a bump out and I had these in my inventory. I hadn’t noticed the orientation and heat damaged one strip with too many attempts since I had installed it upside down. The LEDs were a bit brown and showed signs of lots of heat and wear so I decided to do a full replacement with new strips. The power supply was also brown from heat in the LED controller section. Part number for replacement strips is 2013SVS40F or D2GE-400SCA-R3. The whole TV was also covered in brown dust which is a sign it was in a smoking environment.