This model appears to be a Costco Canada version of UN55F7100 UN55F7100AF. When the power button is pressed, the front LED blinks but the tv doesn’t turn on and there is no backlight. Disconnecting the cable between the main board and power supply, the backlights came on indicating the power supply and backlights were good but the main board was suspect. I sent the board to a repair service on ebay and they indicated the board was good. When I got the board back, I tried powering up the tv with one of the ribbon cables between the tcon and panel disconnected and the tv powered up with one side disconnected. This result indicates there is probably a short on the panel. I did measure low resistance between capacitors on the panel board on the bad side but it would have been extremely difficult to trace a shorted capacitor. I also tried blocking some ribbon connector pins with tape and also removed the side tabs but the tv was a lost cause.
Update: It was likely there were shorted caps on the panel board. I should have had the patience to remove and test every one that appeared shorted.
LG’s LN series comes in a variety of sizes and variations but they all seem to suffer from LED backlight failure. I did a LED replacement of a 60LN5600 which used the thick style lens but replacement was difficult due to the reflector sheet being glued down to the chassis. It was difficult to remove without stretching or ripping it and I had to tape it back down after I replaced the strips. Some of the new replacement lenses were loose and I had to reglue them back on after they were knocked off.
RTRU5528 is the Canadian model and RTRU5527 is the US model.
This tv was reported as having no backlights. Opening up the panel, the backlights tested good with an LED tester. There was a standby light and the tv turned on but without backlight. I then noticed a blown up MOSFET on the power supply board. Some components on the back side were also damaged. Checking other components, D401 was shorted as well. I would recommend checking D401 – D404 and checking the main fuse F101. Power supply part number is HSL55D-2S9.
I have repaired dozens of LG LN series TVs with bad LED backlights. Symptom is the LG logo flashing on power up and the TV is on with sound but no video because the backlight has shut down. Though a LED tester will confirm the failure, it is possible to confirm bad LEDs without one but you need to remove the panel to watch the LEDs flash.
LG Logo Flash on Power Up LG 42LN5700 (looping video – it only flashes once on power up)
The flash is caused by protection circuitry shutting down the backlights because an error is detected in the LED driver circuitry. Driver circuits are current sources driving the leds wired in a series string like Christmas lights. LEDs can fail short (most common) which will cause an undervoltage situation. If LEDs fail open, there will be overvoltage that the driver can detect as well. If there is an open LED, the backlights in that string will not flash. In non-smart LG models, there is no logo and there may just be a quick backlight flash.
The shutdown protects the rest of the LEDs and the power supply. It may also prevent the LEDs from burning up. I have seen LEDs burn up in LN series even with the protection shutdown.
Fire caused by burnt LED LG 50LN5310Burnt LED LG 50LN5750Burnt LED LG 55LF6000
There are a lot of youtube videos on panel removal and I will include one here from Shopjimmy. The panel is extremely fragile and you need to be extremely careful to not crack it. The boards flex connected to the panel can also be ripped off very easily. Damage to the panel or those boards is not repairable.
The TV will turn on with the panel disconnected so you can observe the flashing. By going frame by frame, I took a capture of the flash where you can see two LEDs not lighting up. If you have an LED tester, disconnect the strips from the power supply and probe each strip individually. You can also test LEDs individually with a multimeter in diode test mode but you need to scrape away the solder mask on one side of every LED if there are no test points.
LED backlight flash with the panel removed LG 42LN5700 (looping)Capture of flash where you can see two LEDS not lighting up
LEDs are likely to fail if the backlight level is set to maximum. They get hot and will burn out over time. Failure could occur between 2-5 yrs. On LGs, the default picture modes for Standard and Vivid modes are at 100% level. With the LN smart versions, apps may also default to 100% backlight and can only be changed in the Quick menu.
Repairing Your TV
LED failure is not random and they wear and burn out just like like light bulbs. Proper repair is to replace ALL the strips with NEW ones and to turn down the backlight level. Replacing the individual LEDs or strips is NOT recommended since all the LEDs have wear and the remaining ones are likely to fail in the future. Used strips have wear and will not have the same lifetime as new strips.
It is preferred to have your replacement strips in hand before doing the repair. If your tv has been disassembled for weeks waiting for parts, you may forget how it goes together. You also risk damaging the LCD panel if you haven’t stored it safely and prevented it from gathering dust. However, some models use different panels so may have different strips even for the exact same model number.
To ensure your repair lasts, you need to turn down the backlight level. This setting is in the picture menu. For LGs, 40 to 60% is recommended. With apps, you need to access the Q.Menu to adjust the backlight level. You should check on ALL inputs and ALL apps. I would also recommend turning Energy Saving OFF since this could increase the backlight level in a bright room.
Backlight setting under Picture MenuDifferent menu for apps Q.MenuBacklight setting in Q.Menu
Other LG Series
LB – On these models, the backlights flash when there is a backlight error. Some describe the symptom as flickering but they will flash every two seconds. Strip removal is more difficult since stickier tape is used. Removal may cause the lenses to pop off. Also the lenses are thick and heavy and may also fall off over time leaving bright white spots on the screen. You do have to be careful with substitute strips since the lenses may show halos if not 100% compatible.
47LB6000 Flashing Panel RemovedScreen capture of flash. Notice 5 dim/bad LEDs with 1 visibly burnt up
UH – With a backlight error, it appears these models will shut down and then flash the front LED instead of staying on with the backlight off. With the TV off, you will not see an image with the flashlight test.
Samsung TVs
Samsung TVs also have LED failure but they don’t have shutdown protection. LEDs will fail until there is damage to the power supply or the screen will get very dim. With Samsung TVs, you can disconnect the cable from the main board to the power supply and this will force the backlights on for testing.
You can also set the backlight level on Samsung TVs. Dynamic picture mode will crank the backlights to 100% (level 20/20). It is recommended to set the backlight level between 8-12 to make them last. Eco sensor feature should also be turned off.
NU Series (2018 model) are edge lit from the bottom and have a high rate of backlight failures. See here and here.
Burnt out backlights UN58H5202AF causing failure of Q9101 FET on the power supplyOnly 5 out of 38 LEDs working on Samsung UN40H5203AF
RCA/Proscan/Haier TVs
These models have a protection feature but there is no backlight setting in the menu. However you can turn it down in the service menu under Panel Settings. With the TV on, try Input-1-1-4-7 or Source-2-5-8-0 Be very careful with service menu settings since you can brick your tv. I would check every input and set the backlight to around 60. Some models will have an Energy Saving or Power Saving picture mode which runs the backlights at a lower level.
Sony
Sonys typically will shut down and flash diagnostic blink codes when an error is detected. 6 blinks is typically the error code for bad backlights though it could be different depending on the model. The default backlight level is fairly low in most Sony models and most failures I have seen have come from users setting their picture mode to Vivid which maxes out the backlights. Sonys may not have a separate backlight setting so you need to turn down the brightness.
List of backlight repaired models
LG 32LB5600 32LB5800 42LB5600 42LB5800 42LN5200 42LN5700 42LN5750 43UF6400 43UJ6300 43UH610A 47LN5700 47LN5750 47LB5830 47LB6000 49LB5550 (no shutdown of shorted leds and lenses fall off) 50LA6205 50LB5800 50LB5900 50LB6100 50LB6500 50LN5310 (2 panel versions, Heesung panel has thick style lenses but smaller than LB series) 50LN5400 50LN5700 50LN5750 50UH5500 55LB5800 55LB6100 55LB6300 55LF6000 55UJ6200 55UJ6300 60LB5800 65UH5500
There are a few posts on this model which uses power supply BN44-00787A on Badcaps and a youtube video pointing to Q9101 Q9101C as the culprit. Part is 50R380 (N-Channel, 500V, 14A) Digikey IPD50R380CEAUMA1CT-ND. This transistor fails due to shorted LED backlights. If you just replace the transistor without replacing the LED strips, the transistor will likely fail again. It is recommended to keep the backlight level between 10-14 and never run it at maximum 20.
Update – I have encountered power supplies with a darkened area above Q9102 Q9102C. This part can also short due to bad backlights. The FET is a AOD 5N40 (N-CH, 400V, 5A).
This 4K TV turned on with backligth but no video. Usual suspect in this case is the tcon board. Searching the part on Shopjimmy gets the part number 55.55T12.C02 and I was able to find the board for $20 USD on Ebay from Electroparts online. From the shopjimmy website, this panel is used Sony model XBR-55X900A as well.
With the new tcon installed, the tv was repaired. I did a factory reset and noticed that the default picture mode was set to Energy Saving. In the service menu, source-2-5-8-0 with the tv on, the backlight is set to 34/100 in this mode. In standard mode, it is 58/100. Backlights shouldn’t be an issue in this model if you leave it in these two picture modes.
This tv had a standby light but wouldn’t respond to the power button. I tried freezing the eeprom but that didn’t help either. I ordered a new main board for the tv and the board fixed the problem though I still suspected the old board had an eeprom issue and could be repaired. Eeprom was marked 25Q64B and I ordered some replacements on ebay from China. I read the eeprom off the new board with my CH341 programmer. Once the new eeproms arrive, I will program them and test with the old board.
Update: I was successful in reading the suspect bad eeprom once I removed it from the board so it was unlikely an eeprom issue. With a new eeprom, tv did not turn on so I ended up using the replacement board.
This tv was reported as being dead with no front led and it wouldn’t power up. When I plugged it in, the front led was on but it wouldn’t respond to the power button. Badcaps posts indicated the usual suspects were D607 and C603 on the power supply board. These tested good on my power supply. All voltages appeared stable and present so the main board was getting power. There is an LED on the power supply board itself and it was flashing a 5 blink code. Searching online, I did find an eeprom for this model so I tried freezing it and it made it worse. The front LED was no longer lit after freezing. This test lead me to suspect bad bga connections on the processor.
LG LV series are known for bad BGA though I had read that the LS series had this problem as well. I heated the processor up and when I plugged in the TV, the front led came back and I could turn on the TV. With BGA failures, the lead-free solder balls crack over time and have poor connectivity. Heating up the processor will expand them enough to make contact.
The proper repair in this case is to get the processor reballed which is a bit expensive. I have found previously that baking the board is a temporary fix before the problem comes back. I did try to reflow the IC at 430 deg F with my hot air tool and flux but it didn’t work.
I was able to find a used board online but the problem may reoccur with a used board.
This TV turned on with no backlight. I found four intermittent LEDs on one strip and replaced them with 3V Samsung compatible ones. To turn down the backlight, you need to go into the service menu. For this model, with the tv on, push source-2-5-8-0 on the remote and the backlight level is under Panel Settings. I set it to around 55. This value needs to be set on EVERY input and may apply to only the current picture setting (Standard, Energy Saving, Dynamic, User).
Update: I got another of this model in. I was having repeat failures on a bottom strip. Since it was difficult to find even a used strip (part# DLED55LS 5×10 0005 A-1 and A-2), I ended up replacing every LED module on that strip.
With this model there is a setting called DLC (Dynamic Light Control) which is on by default. I would turn this off so the backlights do not go bright in a bright room. You need to to set this on every input. I also found the backlight settings very high so adjusted the backlight level to 10. Again this needs to be done on every input.
Update 2: I replace every LED on the strip and they are still burning out after several hours. This model appears to run the backlights at very high current even with the backlight level turned down. I have ordered some 2W (700mA) replacement LEDs since the strips can’t be found online.
This TV had a standby light but wouldn’t turn on. Unplugging the main board from the power supply would force the backlights on so both the backlight and power supply appeared good. I took a can of duster, inverted it, and sprayed it on the flash IC. With the flash frozen, the tv turned on.
The main board part number is BN94-06429C (BN94-05429C and BN94-05429D may be compatible. I was not able to find any of these used boards on ebay.
I considered replacing the flash module but didn’t have a programmer. It was also suggested the BGA nand module would also be replaced.
I suspected main boards from model UN46D6000SF would be compatible. Shopjimmy shows a large number of substitutable main boards for this model and also a few different panel numbers. None matched my number, LD460CGB-A2. Checking specs and pictures, UN46D6000 has 2 more HDMI ports, 2 more USB ports and VGA and ethernet connectors not available on UN46D6003.
I gambled on one board but had to return it because the connector to the front panel was different (larger black instead of white). The second board I ordered was a match and it worked.
After installation, I made sure the firmware was upgraded and performed a factory reset.
