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Old 10-11-2021, 01:53 PM   #1
htv239
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Default LG UH8500 Backlight Troubleshooting Help

Hello,

I am currently troubleshooting an LG 60UH8500 TV (2016 TV). Any help or suggestions would be appreciated.

Overall Issue: When TV is turned on, backlights all come on for about 10 seconds, then all go out. There is sound and there is a picture on the display (obviously hard to see without backlights, but it is there).

What I Have Done So Far: 1) Removed the back TV cover to expose the boards (Power Supply, Tcon, and Main), 2) blew out any dust and cleaned all connections, 3) Noticed that the LED backlights are fed from two separate connectors (one is BLK and the other is WHT) from the Power Supply Board (BLK corresponds to the LEFT side lights facing the back of the TV, WHT corresponds to the RIGHT side lights facing the back of the TV for convention). So I disconnected each one, one at a time and tried to power it up. With the BLK connector connected and WHT connector disconnected, the TV powered up fine, the LEFT (corresponding to the BLK connector) backlights turned on fine and stayed on. Basically, a normal TV with the RIGHT half of the backlights out (expected, since I had the RIGHT (WHT) half of the backlights intentionally disconnected). Then I switched the connectors so that the BLK one was disconnected and the WHT one was connected. Powered it on and saw RIGHT backlights come on briefly and then go out (obviously the LEFT backlights never came on since they were disconnected).

This all leads me to believe that there are bad LED(s) on the RIGHT half associated with this WHT connector.

I really, really, do not want to disassemble the TV so I bought a Power Supply Board off of EBay, and swapped the board out. Same exact issue, so this did not help.

One thing I did notice is that with both BLK and WHT connectors connected during the startup is that the Power Supply Board LD701 (which I think is a troubleshooting LED) blinks 4 times periodically. I think this is an error code. But, for the life of me, I cannot find the code matrix for this anywhere on the internet. I know when I have one of the connectors disconnected, this LD701 blinks 3 times periodically so I’m guessing 3 blinks = open LED circuit. But what does 4 blinks mean?

I think I am pretty much into an LED strip replacement, but am in denial since that is such a painful process.

For completeness, there are LED+/- test terminals on the Power Supply Board so I measured this voltage during the three main scenarios:

1) Both BLK (LEFT) and WHT (RIGHT) LED connectors connected, powering on: LED+/- voltage rises from a standby 43 VDC to around 100 VDC, all backlights come on for around 10 seconds, voltage decays to around 63V, all backlights go out, error LED (LD701) blinks 4 times periodically.

2) BLK (LEFT) LED connector connected, WHT (RIGHT) LED connector disconnected, powering on: LED +/- voltage rises from a standby voltage of 43 VDC to around 100 VDC, LEFT backlights all come on and stay on, voltage decays to around 80 VDC, error LED (LD701) blinks 3 times periodically (probably because I have the WHT connector disconnected and it detects an LED open circuit).

3) BLK (LEFT) LED connector disconnected, WHT (RIGHT) LED connector connected, powering on: LED +/- voltage rises from a standby voltage of 43 VDC to around 100 VDC, RIGHT backlights all come on for about 10 seconds and then go off, voltage decays to around 63 VDC, error LED (LD701) blinks 4 times periodically.

I do have an LED tester and I will be testing LED lights as best I can before disassembly.

My biggest questions really are:

1) Shake me out of denial and agree this is a bad LED(s) on the WHT (RIGHT) side somewhere,

2) Does anybody have or know where the LG Power Supply Board troubleshooting LED LD701 decoder matrix is for the number of blinks corresponding to the detected problem? I mean, specifically what does 4 blinks mean!!!???
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Old 10-11-2021, 03:13 PM   #2
neilc6
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Default Re: LG UH8500 Backlight Troubleshooting Help

UH series has bad backlights, symptom is flash of backlights or no backlights. Protection circuit kicks in and shuts them down if even one is detected bad. Just replace all the strips with new and turn down the backlight level after replacement. 80% of TVs I repair have bad backlights and 99% of bad backlights are burnt out LEDs though bad LEDs can damage power supplies in models without protection (Samsung). Bad LEDs may also test good with a LED tester since they may fail at higher operating current.

Looks like your model is edge lit. Very difficult repair and very finicky.

Last edited by neilc6; 10-11-2021 at 03:20 PM..
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Old 10-11-2021, 04:53 PM   #3
htv239
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Default Re: LG UH8500 Backlight Troubleshooting Help

Yep, it is edge lit. You are correct on all fronts. I used the LED tester and got the suspect LED lights to illuminate but I saw that the driving voltage was lower than the TV normal operating voltage, so I don't take anything away from that. I know that is a finicky repair and hence "denial".

For full disclosure, I already ordered two new LED strips but was hoping for a miracle.
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Old 10-18-2021, 06:52 PM   #4
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Default Re: LG UH8500 Backlight Troubleshooting Help

Just to close this thread, I did change the backlights, put the TV back together, and it is now working well. In case anybody can use this information, this LG 60UH8500 is edge-lit, and has two LED strips side by side on the bottom. When I went into this, I was not sure how many strips there were and where they were located. I guessed and bought two. Also, I was able to replace both LED strips (one was bad but I did both) without removing the heat sink that they were adhered to. So, the disassembly was painful (not difficult, but time consuming and very slow to keep from breaking anything), but changing LED strips themselves was pretty easy once you finally got the strips exposed.
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Old 10-18-2021, 08:05 PM   #5
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Default Re: LG UH8500 Backlight Troubleshooting Help

Turn down your backlight level and turn off energy savings mode to make your new strips last. Check every input and every app.
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Old 10-19-2021, 09:02 AM   #6
htv239
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Default Re: LG UH8500 Backlight Troubleshooting Help

Yep, I now have a greater appreciation for backlight preservation after just going through that exercise. So, I made sure all of the TV settings were optimized afterwards. I never thought of apps--I just assumed brightness, etc. was all controlled through the TV. For example, do NETFLIX, PRIME, Firestick settings also make the backlights higher duty if you do not adjust their individual app settings??? I will go into their settings and see what is there. Thanks!
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Old 11-13-2021, 05:33 PM   #7
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Default Re: LG UH8500 Backlight Troubleshooting Help

Quote:
Originally Posted by htv239 View Post
Just to close this thread, I did change the backlights, put the TV back together, and it is now working well. In case anybody can use this information, this LG 60UH8500 is edge-lit, and has two LED strips side by side on the bottom. When I went into this, I was not sure how many strips there were and where they were located. I guessed and bought two. Also, I was able to replace both LED strips (one was bad but I did both) without removing the heat sink that they were adhered to. So, the disassembly was painful (not difficult, but time consuming and very slow to keep from breaking anything), but changing LED strips themselves was pretty easy once you finally got the strips exposed.
Hello friend
Have you recorded or have a description on
How you changed the edge light?
Best/ Mads
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Old 11-13-2021, 11:51 PM   #8
RJARRRPCGP
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Default Re: LG UH8500 Backlight Troubleshooting Help

The backlights sound just as unreliable as on the UH6100s. We had a UH6100 of the same build year and the backlight LEDs were clearly bad, (purplish-blue) even when it didn't shut off the backlight LEDs.

My sister started using it in 2018 and the backlight LEDs were very obviously bad by 2021.

(even when we got it in 2017 and I tried it for gaming, because I didn't know if they were actually that bad or not, but even before the backlight LEDs went bad, they were piercing my retinas!) (Never that model, ever again! With the fact that it has LCD-RGBW "4K" and premature backlight LED failure!)

Albeit it looked good at 1080p, before the backlight LEDs failed.
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Last edited by RJARRRPCGP; 11-14-2021 at 12:00 AM..
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Old 11-16-2021, 04:20 AM   #9
MadsJ
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Default Re: LG UH8500 Backlight Troubleshooting Help

Hello friend
Have you recorded or have a description on
How you changed the edge light?
Best/ Mads
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Old 11-16-2021, 04:36 AM   #10
MadsJ
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Default Re: LG UH8500 Backlight Troubleshooting Help

Quote:
Originally Posted by htv239 View Post
Yep, I now have a greater appreciation for backlight preservation after just going through that exercise. So, I made sure all of the TV settings were optimized afterwards. I never thought of apps--I just assumed brightness, etc. was all controlled through the TV. For example, do NETFLIX, PRIME, Firestick settings also make the backlights higher duty if you do not adjust their individual app settings??? I will go into their settings and see what is there. Thanks!
Hello friend
Have you recorded or have a description on
How you changed the edge light?
Best/ Mads
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Old 11-16-2021, 04:36 AM   #11
MadsJ
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Default Re: LG UH8500 Backlight Troubleshooting Help

Hello friend
Have you recorded or have a description on
How you changed the edge light?
Best/ Mads
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