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UN65MU6290 No Backlight

UN65MU6290VXZA UN65MU6290VXZC

I researched this model thinking I could repair it since I had salvaged parts from a cracked screen TV. Apparently, there are two different versions. UN65MU6290F and UN65MU6290V. The V version is edge lit and is very prone to backlight failure. Shopjimmy recommends replacing two resistors to limit the backlight current after LED replacement. This ebay post from a backlight seller indicates bad LEDs can damage the power supply and bad power supplies can damage the LEDs.

“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. “

This ebay listing indicates the LED driver IC IC9101 SEM4082A can fail as well as Q101c and Q201c.

On top of all these potential issues, the back cover is screwless and needs to be pried apart. There are holes at the bottom to insert a tool to start prying apart.

LG 32LK450-UB No Backlight

This LCD tv turned on but without a backlight. Googling found a repair kit for transistors on the inverter board.

Testing the transistors on the inverter board, I found Q103 (Nikos P4004ED PCH, 40V, 21A) shorted and F101 (240V, 7A) blown. Replacing both parts restored the backlight. If Q105 or Q107 are shorted, the part is P2904BD (NCH, 40V, 25A).

Samsung UN55F7050 Won’t Turn On

Model UN55F7050 UN55F7050 AF UN55F7050AFXZC

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 60LN5600 LED Backlight Replacement

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.

RCA RTRU5528 No Backlight

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.

Here is a list of parts replaced
Q506 & Q507 TF5N50 (NCH 500V 5A) Digikey FDPF8N50NZ-ND (8A substitute)
Q504 & Q505 (2T marking) MMBT4403 (PNP 40V 0.6A) Digikey MMBT4403LT1GOSCT-ND
D509 (T4 marking) 1N418 100V 0.3A Digikey 1N4148W-FDICT-ND
R506 240 ohm 1206 Digikey 311-240FRCT-ND
R533 & R528 30 ohm 1206 Digikey 311-30.0FRCT-ND
D401 SF26 400V 2A Digikey 1655-1581-1-ND
F101 4A 250V fuse Digikey 507-1721-1-ND

LG LN Series Bad LED Backlights

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)

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 series 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 may not flash at all. 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.

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.

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.

Repair Options

  1. Full replacement of all strips with NEW ones. This option is preferred to minimize future problems with your backlights. Reputable sellers include Shopjimmy and ebay seller meihua361000 based in China. I have had failures with Rzconne branded strips so best to avoid those.
  2. Replace bad strips with used ones. This option is cheaper if you have used strips but if you are buying strips, its only a bit more for new ones. Because there is wear on the existing LEDs, they may fail in the future.
  3. Replace the LED itself. The LEDs are pretty cheap but you could have an issue with centering the lens back on. If not perfect, it can cause bright spots. For the LN series, you can find 3V 2835 LG replacements on Aliexpress.

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, 50 to 70% is recommended. With apps, you need to access the Q.Menu to adjust the backlight level. You need to do 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.

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 10-14 to make them last.

Burnt out backlights UN58H5202AF causing failure of Q9101 FET on the power supply

RCA/Proscan 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-2-4-8-0 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.

List of backlight repaired models

LG 32LB5600 42LN5700 42LN5750 47LN5700 47LN5750 50LA6205 50LB6100 50LB6500 50LN5310 50LN5400 50LN5700 50LN5750 55LB5800 55LB6100 55LF6000

Vizio E60-C3

Samsung UN40EH5300F UN40H5203AF UN46H5203AF UN46EH5300F UN50EH5300F UN55D6300SF UN55FH6030 UN55ES6100F UN60ES8000F

Haier 40D3505

Insignia NS-37D20SNA14 NS-55D550NA15

RCA/Proscan RTU5540-D RLDED5078A-D RLDEDV3988-A EP5585 SRC5565

UN58H5202AF No Backlight Doesn’t Turn On

UN58H5202 UN58H5202AF UN58H5202AFZXC

There are a few posts on this model 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.

Shorted LEDs in Samsung UN58H5202AF

Element ELUFT551 No Video

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.

Haier 48D3500 Doesn’t Turn On

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.

LG 47LS4500 No Power

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.