LG 50UH5500-UA - No picture

[tcbr453]

We have a LG 50UH5500-UA which has stopped working.

When first plugged in, press power button... LG logo appears for less than a second, then screen goes black. The red light at the power button also comes on, turns off, then blinks twice.

Watching from the back with the cover off, the backlight quickly flashes on and then off. A red light on the main board under the heat sink turns on and then off, as does the red optical port light. Subsequent attempts at powering on the TV without unplugging it first will show the same except the backlight never comes on, and the logo doesn't appear. If I unplug the TV and let it sit for a minute, then next attempt at powering on will produce the brief logo again.

Have replaced power board. Cleaned and reseated connections. Tried flashlight test, could not see any picture. Tried baking main board for 10 minutes at 385F.

No burns or obvious issues visually apparent in TCON or main board. Cables all seem intact.

Any ideas where to go from here? I've seen suggestions for similar issues for both main board and LEDs...

Pictures are attached and also here.

Thanks!

[Andrew F. Ali]

Re: LG 50UH5500-UA - No picture

Hopefully you did not damage a good working Main Bd by baking it. I personally do not believe in baking a board. Though I have read posts on the site where others have baked with success.
OK. Your issue seem to be bad LED backlights. Measure the voltages on the LED backlight connector on the PSU at start-up. The voltage should spike to about 195Vdc and then settle to around 90Vdc, if the LED Driver circuits are good. You would be using the BLACK lead to chassis GND and the RED lead of your DMM to Pins 1 to 6. Report your findings.

[hutchr]

Re: LG 50UH5500-UA - No picture

I have the exact same issue with this model tv. I did replace the power board as well. With the new board i have 90V at the led driver. you can measure this voltage across the capacitor near the connector that goes to the led lights. When I turn the tv on the voltage drops to around 58V. Any further information on this tv would be greatly appreciated.

[dick_barton]

Re: LG 50UH5500-UA - No picture

Disconnect the led connector then power up out of standby and check if the voltage at that connector peaks to around 190V as indicated in post #2

[Mosijoon]

Re: LG 50UH5500-UA - No picture

We have a LG 50UH5500-UA which has stopped working.

When first plugged in, press power button... LG logo appears for less than a second, then screen goes black. The red light at the power button also comes on, turns off, then blinks twice.

Watching from the back with the cover off, the backlight quickly flashes on and then off. A red light on the main board under the heat sink turns on and then off, as does the red optical port light. Subsequent attempts at powering on the TV without unplugging it first will show the same except the backlight never comes on, and the logo doesn't appear. If I unplug the TV and let it sit for a minute, then next attempt at powering on will produce the brief logo again.

Have replaced power board. Cleaned and reseated connections. Tried flashlight test, could not see any picture. Tried baking main board for 10 minutes at 385F.

No burns or obvious issues visually apparent in TCON or main board. Cables all seem intact.

Any ideas where to go from here? I've seen suggestions for similar issues for both main board and LEDs...

Pictures are attached and also here.

Thanks!

Hello. Any luck with Finding the problem? I'm having exactly same problem. Power board pins which are supposed to be 13 V jumps between 9.5 V to 11.5 V.

[philtvman]

These LG's are notorious for LEDs burning out, I'd bet money that's the issue.

[Mosijoon]

Re: LG 50UH5500-UA - No picture

These LG's are notorious for LEDs burning out, I'd bet money that's the issue.

Thank you for your reply. I doubt it's burnt LEDs, because there is no picture with flashlight test. Like this thread he had the same issue but it wasn't the LEDs: https://www.badcaps.net/forum/showthread.php?t=69687

Moreover, It shows the logo then turns off.

[neilc6]

Re: LG 50UH5500-UA - No picture

LG LED TVs that flash the logo and turn off is a symptom of bad LEDs in the backlight. Circuitry detects a problem and then shuts down the backlight circuit. I have repaired quite a few.

[neilc6]

Re: LG 50UH5500-UA - No picture

LG LED TVs that flash the logo and turn off is a symptom of bad LEDs in the backlight. Circuitry detects a problem and then shuts down the backlight circuit. I have repaired quite a few.

Actually the TV doesn't turn off, just the backlight. The TV stays in an on state.

[DXseekerMO]

Re: LG 50UH5500-UA - No picture

I just bought this exact same model TV with the exact same problem. I'll be tearing it down this week to see how many LED's are now looking up at the grass!

[Mosijoon]

Re: LG 50UH5500-UA - No picture

LG LED TVs that flash the logo and turn off is a symptom of bad LEDs in the backlight. Circuitry detects a problem and then shuts down the backlight circuit. I have repaired quite a few.

So if it's the LEDs why can't I see any picture using the flashlight? Isn't it always the case? And why the voltages in 13 V pins jumps around? Sorry for too many questions, I'm not an expert.

[budm]

Re: LG 50UH5500-UA - No picture

What DCV do you see on 13v PIN when TV is OFF?
We also need the list of Voltages of all the pin of the connector of the power supply that goes to the main board when TV is plugged in and when power switch is activated, you MUST pin down pin name and follow by the Voltage reading for each pin so we can easily see what you have and do not have on each pin.

[DXseekerMO]

Re: LG 50UH5500-UA - No picture

I just bought this exact same model TV with the exact same problem. I'll be tearing it down this week to see how many LED's are now looking up at the grass!

Before you presume your TV has the same problem as mine, please, follow the troubleshooting advice given you by the more senior members like budm before disassembling your set. Mr. Martin is a very patient person, he's trying to teach everyone something and I don't want to get in the way of that.

Secondly, this TV has booby traps in it. While removing the thin plastic buffer board protection sheet to remove the buffer boards I found a piece of tape on the left side (TV upside down) that was placed around the buffer board and taped to the protection sheet in such a way that if one tried to forcefully remove the protection sheet there it could break the board or rip the tab bonds off.

Secondly, the bottom diffusion sheet, the thick plastic one is double sided taped to the reflector sheet at the top.

Third, the diffusion sheet itself is double-sided taped to the chassis and requires a gentle touch to remove. Four rows of the LED strip retaining screws must also be removed to release the reflector sheet. It has slots in it for the clear plastic diffusion supports so they did not need to come off.

Now for what I found: My TV has ONE STINKING BAD LED! That's it. It failed open causing both center rows of backlights not to illuminate.

Now I need to find out which LED's these use so I can get some lamp beads and put my LED re-work station to good use!

[neilc6]

Re: LG 50UH5500-UA - No picture

Now I need to find out which LED's these use so I can get some lamp beads and put my LED re-work station to good use!

These are the ones I am using from Aliexpress. Pay the extra for Aliexpress Standard Shipping.

https://www.aliexpress.com/store/pro...794780330.html

[DXseekerMO]

Re: LG 50UH5500-UA - No picture

Thanks for the link. Those are a large pad anode/small pad cathode and the LED's this strip has on it are the opposite.

[DXseekerMO]

Re: LG 50UH5500-UA - No picture

....and they call me.....Threadkiller

[Mosijoon]

Re: LG 50UH5500-UA - No picture

Before you presume your TV has the same problem as mine, please, follow the troubleshooting advice given you by the more senior members like budm before disassembling your set. Mr. Martin is a very patient person, he's trying to teach everyone something and I don't want to get in the way of that.

Secondly, this TV has booby traps in it. While removing the thin plastic buffer board protection sheet to remove the buffer boards I found a piece of tape on the left side (TV upside down) that was placed around the buffer board and taped to the protection sheet in such a way that if one tried to forcefully remove the protection sheet there it could break the board or rip the tab bonds off.

Secondly, the bottom diffusion sheet, the thick plastic one is double sided taped to the reflector sheet at the top.

Third, the diffusion sheet itself is double-sided taped to the chassis and requires a gentle touch to remove. Four rows of the LED strip retaining screws must also be removed to release the reflector sheet. It has slots in it for the clear plastic diffusion supports so they did not need to come off.

Now for what I found: My TV has ONE STINKING BAD LED! That's it. It failed open causing both center rows of backlights not to illuminate.

Now I need to find out which LED's these use so I can get some lamp beads and put my LED re-work station to good use!

Thank you so much for the write up. I repaired my TV. It was one freaking LED. However, I didn't have the equipment to replace an individual LED so I bought a strip for cheap from ebay. Oh god, how many tapes I had to remove to get in to the LEDs! there were tapes all over that thing.

As you can see in the picture the old led strip has a yellowish tint around each led due to the high temperature. No wonder this model is notorious for burning out LEDs. The backlight setting in on 100% by default on the most of the picture modes.

[laptopservice]

Re: LG 50UH5500-UA - No picture

reball the BGA chip

[nwcs]

Re: LG 50UH5500-UA - No picture

I found that two of the wires one led- and one led+ were unseated from the power supply. After making sure they were in the tv now has backlight but one side is darker than the other. I hope it is not a bad panel and think it might be a bad tcon. Does any one have a suggestion?

[Davi.p]

Re: LG 50UH5500-UA - No picture

1. Nwcs please dont hijack other's thread with different issues! Open anew thread..
2. I dont trust much to backlight problems with the OP's symptoms.. why? If i'm not wrong watching the PSU picture i see the mainboard connector pins: ENA - ADJ, GND -GND, 13V - 13V, 13V - 13V, GND - 13V, STB - NC. So there's no error signals that tell the main board BL problems and it shuts off the tv. I think some of you didnt tell the truth, i trust instead of a spi flash problem on mainboard...