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.

Here is a parts list

U807 CS8N65F sub FDPF8N50NZ (NCH, 500V, 8A)
C822 – 100pF 1KV
R818 – 0.39 ohm 1W
N834 – NCP1271A NCP1271D65R2GOSCT-ND‎ Digikey

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.

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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.

This TV turned on with no backlight. Since there was no backlight flash, there was possibly an open LED in the string. Westinghouse uses the same white label Chinese TVs as RCA, Proscan, Haier and many other brands. The firmware in these sets do not give the user the ability to adjust the backlight level.

This TV was difficult to open up. The outer bezel was held in place by screws and metal tabs that had to be released by sliding a black plastic tab. It was also double sided taped to the panel. In this scenario, I leave the bezel attached to the panel when removing it.

Once open, I found one open LED which I replaced with a Samsung-compatible 3V module. All the LEDs were a bit brown showing signs of both heat and wear. The backlights were wired as one long string with 4 rows of LEDs. Once assembled, I tried the usual combination for RCA TVs to get into the service menu to turn down the backlight level but was unsuccessful. Googling found a working code. With the TV on, press menu-0-0-0-0 on the remote. To get to the backlight setting, go to Other -> Panel Settings. The default value setting for Energy Savings was very high at 90. I reduced to 55 which saved it under User picture mode. This step needs to be done on all inputs.

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This TV would turn on with no backlight and no video. I could heard sound effects when I moved the toggle button which confirmed the main board was working and the TV was on.

I first suspected bad backlights which is the case for 90% of Samsungs with no backlight. Unplugging the main board cable at the power supply end forces the backlights on and they came on. This test confirmed both the power supply and backlights were good.

I checked the BL_ON signal from the main board and it was high as well indicating the main board is likely working. On this model, there is an extra cable from the power supply to the tcon board which appears to control the backlight on signal.

The tcon board only had two out of three LEDs lit up and when disconnecting both ribbons to the panel, the third LED still did not light up. Powering up the TV with only one side connected at a time also did not produce backlight nor picture. This test indicates there is no panel fault and the tcon is suspect.

I ordered a tcon on Aliexpress and with the current shipping delays, it may be a few months until the part arrives.

Update: Tcon board finally arrived and TV powers up with backlight and video. The new tcon lights up with 3 LEDs.

This TV has a standby light but wouldn’t turn on or respond to the on/off button on the remote or side buttons. I was able to get it turn on randomly however.

Typically the suspect in these cases is the main board. I froze the EEPROM with an upside down can of duster and was able to get it turn on a few times. The part number for UF1 was W25Q16BSIG (16Mbit flash). I was able to read the contents with my CH341 programmer and I experimented by programming it into W25Q64BV (64Mbit) flashes I had. With new and larger flash installed, there was no standby light. I erased the original flash, reprogrammed it, and reinstalled it and it does appear fixed.

I have ordered the 16Mbit ICs in case the TV comes back with the same problem. I also turned down the backlight in the service menu to level 60. In this model, it needs to be done on all inputs and is saved under the User picture mode.

The owner indicated the flashlights were flashing which typically is a sign of failing backlights. I had asked them to turn down the backlight level and it was fine for a few weeks before the picture went dim. Testing the strip, 5 out of 68 LEDs were bad so I replaced the single strip. Powering up the TV, they would flash on power up before shutting off though they were all lighting up. The strips are wired as 4 banks of 17 LEDs and each bank tested good and measured 51V on my LED tester (3V LEDs). I have run into the issue of bad LEDs damaging the power supply so suspected the controller IC may have been damaged as well.

Searching online, there are a few reports of the OZ9998HDN IC overheating and needing replacement with symptoms of a flashing backlight.

I ordered the ICs from Aliexpress and the power supply did not turn on the backlights with both ICs that I installed. I ended up buying a new power supply board and this finally fixed the TV.

50L3400U is a similar model. I have run into this problem before with Toshibas where there is both LED and power supply damage.