Question LG 65UF6450 - Won't power on, no backlight

[dj505]

Hey! First post here, hope this is the right place.

Some backstory - this TV was given to me by a friend, it was having issues and they ended up getting a new one. It survived a lightning strike a couple years ago and worked fine for a year and a half or so after, before it started to experience glitchy screens and other very obvious issues. By the time it got to my house, plugging it in and powering it on would flash the LG logo, which only worked a few times. Now the only thing that happens is what's described below. I'm on a really strict budget for this project, so ordering replacement boards is something I'd like to avoid if possible.

When plugged in, the red standby light is lit, and when attempting to power on the TV with the remote, it flashes a few times before going dark. There's no picture and the screen doesn't light up at all. When using the remote to turn it off again, the red standby light turns back on, so it's at least responding to the remote. I tried taking out the main board and putting it in the oven at 385 Fahrenheit for about 10 minutes, which seemed to be a popular fix - but it there was no difference after putting the board back in. Maybe it's because my oven hasn't been heating up properly, or maybe the issue is something else entirely. The frustrating part is that I don't have the equipment to be able to narrow it down properly.

I tested for continuity on both fuses (that I could find) on the power supply, and both were fine, not blown or anything. I also attempted to test the power supply output with a multimeter, and where there should have been 13.2v, I got a 0v reading. I've never used a multimeter for this before so maybe it was just connected wrong. I accidentally bridged the 13.2v pin and ground pin for a fraction of a second, which let some sparks out, but it wasn't for long; hopefully I didn't damage anything. Next up I plan to test the LED backlight voltages to see if maybe it's a backlight problem, which I doubt is the case but I guess it's worth a try.

Edit: When plugged in, hitting the power button on the TV turns on a red LED on the main board, so I believe the power supply board is okay. Still no picture or backlight, though. Pressing one of the 2 small buttons on the main board turns off the TV and also flashes the backlight, so I don't think the backlight is damaged. Maybe the main board needs to be properly reflowed?

Any suggestions would be really appreciated! I really want to get this thing up and running again.

 

[howsthat]

See if you can see any display on the screen with a flashlight , hit menu on remote, look closely see if you see the menu or anything with the flashlight, it very well could be a backlight led problem.

 

[dj505]

See if you can see any display on the screen with a flashlight , hit menu on remote, look closely see if you see the menu or anything with the flashlight, it very well could be a backlight led problem.

Tried it out, when shining my phone's flashlight on the screen there's something there, but not what's supposed to be there - the left half of the screen seems to turn white for a second or two before turning black again for another second or two, over and over. There's no text or anything that I can make out, either. The backlight LEDs work at least, since one of the small buttons on the main board flashes them when pressed

 

[howsthat]

You can verify your meter working correctly by testing a 1.5 or 9 volt battery, set meter to 20 vdc and put a probe on each terminal. Test connector P201 from mainboard to powerboard on powerboard side with all boards hooked up, should be a little legend/map of pin description and expected voltages near the connector, looks like you will be testing 12 pins, test with tv plugged in but off then hit power, report both conditions here, give pin number, pin description/name and condition both off and when you hit power on. Set meter to 20 vdc negative probe on metal tv chassis, positive probe on each pin, example here:

View: https/www.youtube.com/watch?v=4v8DcqCNG4A

 

[dj505]

You can verify your meter working correctly by testing a 1.5 or 9 volt battery, set meter to 20 vdc and put a probe on each terminal. Test connector P201 from mainboard to powerboard on powerboard side with all boards hooked up, should be a little legend/map of pin description and expected voltages near the connector, looks like you will be testing 12 pins, test with tv plugged in but off then hit power, report both conditions here, give pin number, pin description/name and condition both off and when you hit power on. Set meter to 20 vdc negative probe on metal tv chassis, positive probe on each pin, example here:

View: https/www.youtube.com/watch?v=4v8DcqCNG4A

I'll give that a try asap! I may not have time tonight but if I do I'll make sure to report back. Otherwise I'll have to test it out tomorrow. I wasn't entirely sure how to test that all with my multimeter, so this really clears things up. Thanks!

Edit: I'm getting the right voltages where they're supposed to be, 13.2v on each output according to the small table printed under the connector, so it seems the power board is fine! There are many fewer pins on mine compared to the one in the video, and they seem to be outputting properly. I tested GND and 13.2v primarily, haven't tested the PWR ON pins yet.
There are 6 pins, which from top to bottom are

	TV Off	TV On
PWR ON	0V	75mV
GND	0V	0V
13.2V	0V	13.2V
13.2V	0V	13.2V
GND	0V	0V
PWR ON	0V	75mV

If necessary, I can re-test the connections when the TV is off since I didn't write them down and only went off of memory for most of those, mainly the GND connections.

 

[howsthat]

As always BE VERY CAREFUL when working with power supply the HOT/PRIMARY side has DEADLY voltages.

 

[dj505]

As always BE VERY CAREFUL when working with power supply the HOT/PRIMARY side has DEADLY voltages.

Made sure not to touch anything on that side, all the videos I watched said the same thing lol. Is there anything else I can do from here on out to get this thing working? Now that I know the power supply is fine, I suspect something is wrong with the main board but I don't know how to fix it.

 

[howsthat]

Ok, not sure if this tv has pull-up resistors, can try a test: with power cord unplugged( is good policy to have power cord unplugged whenever unhooking any connections so nothing gets shorted accidentally) unhook cable from powerboard to mainboard, then plug the power cord back into powerboard with that other cable still unplugged, see if the backlights come on.

 

[dj505]

Ok, not sure if this tv has pull-up resistors, can try a test: with power cord unplugged( is good policy to have power cord unplugged whenever unhooking any connections so nothing gets shorted accidentally) unhook cable from powerboard to mainboard, then plug the power cord back into powerboard with the that other cable still unplugged, see if the backlights come on.

Main board is disconnected from the power board, no backlight when I plug it all in

 

[howsthat]

Kind of hard to tell from your test but it looks like the mainboard is not sending the power-on or drv-on signals to the powerboard.

 

[howsthat]

Try testing those pins again with the cable unhooked and power cord plugged into powerboard.

 

[howsthat]

Mainboards can be tough to fix, usually always at least requires some soldering, you could take it out and check over the solder joints on the bottom side for cold/bad solder joints.

 

[howsthat]

I see a couple mainboard services on Ebay where you send them your board and they fix it for $99, looks like a few mainboards there for $150 or so also.

 

[dj505]

I see a couple mainboard services on Ebay where you send them your board and they fix it for $99, looks like a few mainboards there for $150 or so also.

$99 even is a lot, I'll have to think about it before sending it in. I'm just about to test the connections with the main board unplugged and I'll get back to you after that. I'm fairly confident in my soldering abilities but I definitely don't have the tools to reflow or solder BGA chips lol. Thanks a ton for your help, I really hope I'll be able to get this fixed soon

Edit: With the main board unplugged, there's no voltage on the 13.2v pins at all, which is pretty much the same result as when I test those pins with the TV off. Nothing on PWR-ON either.

 

[howsthat]

Lots of reflow tutorials on youtube, correct proper fix is to reball the bga chip thats if it is the culprit. Otherwise some use a heatgun to heat the chip up, they claim it only lasts a few weeks to a few months tho, some attach fans, one guy made a hole in his back cover about where the bga chip is and attached a fan and hasn't had a problem, I think the trick is to keep that chip from getting too hot and acting up again.

 

[dj505]

Lots of reflow tutorials on youtube, correct proper fix is to reball the bga chip thats if it is the culprit. Otherwise some use a heatgun to heat the chip up, they claim it only lasts a few weeks to a few months tho, some attach fans, one guy made a hole in his back cover about where the bga chip is and attached a fan and hasn't had a problem, I think the trick is to keep that chip from getting too hot and acting up again.

I'll try blasting the chips with a heat gun later today when I have some more time, just watched a few tutorials on it and it doesn't seem too bad at all. I'll report back and let you know how it works - not like I can break this TV any more than it's already broken, haha. Thanks again for your help!

 

[howsthat]

Here's a little better description for when it's the bga problem: The processor soldered to the board uses whats called BGA or ball grid array. The TV and processor get hot, then cool when turned off. Over time this heating/cooling cycle causes small cracks in the solder. These cracks are not visible to the naked eye and BGA is not easily fixed, requiring specialized equipment. There are 3 things you can do: 1. Do whats in this video, but its a temporary fix that wont last. 2. Purchase a new mainboard 3. Have a company that has the equipment to work with BGA remove the processor, remove all the solder and resolder it back to the mainboard.

 

[dj505]

Here's a little better description for when it's the bga problem: The processor soldered to the board uses whats called BGA or ball grid array. The TV and processor get hot, then cool when turned off. Over time this heating/cooling cycle causes small cracks in the solder. These cracks are not visible to the naked eye and BGA is not easily fixed, requiring specialized equipment. There are 3 things you can do: 1. Do whats in this video, but its a temporary fix that wont last. 2. Purchase a new mainboard 3. Have a company that has the equipment to work with BGA remove the processor, remove all the solder and resolder it back to the mainboard.

That about sums up what I found while researching a bit lol, I definitely don't have the tools to properly reball the BGA. I'm fine with a temporary fix as long as it means the TV runs again - if it does, I'll consider getting it repaired professionally, I just want to know that it still functions first before spending a bunch of money. Gonna try the heat gun fix and see how it goes!

 

[howsthat]

I think the trick is get it up to 220 c, for about 20 seconds or so, they say bring it up to temp slowly then after move the heatgun away slowly to try to reduce the possibility of thermal shock, check out badcaps.net, some pretty sharp techs on there, my name is nomoresonys over there.

 

[dj505]

I think the trick is get it up to 220 c, for about 20 seconds or so, they say bring it up to temp slowly then after move the heatgun away slowly to try to reduce the possibility of thermal shock, check out badcaps.net, some pretty sharp techs on there, my name is nomoresonys over there.

Tried it out, either my heat gun just doesn't get warm enough or it didn't work, same set of issues as before I was focusing on the main processor after removing the heatsink, but maybe the cause lies elsewhere?

Edit: My heat gun only goes up to 165 Celsius, not nearly hot enough unfortunately, I'm gonna have to find another solution