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Old 10-16-2019, 11:49 AM   #1
slip
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Default LG 50UH5500 - Display won't stay on

I checked the forum and found another thread that is very similar from tcbr453. I have the same TV but I want to check with you guys before I get down to the LEDs (which I also would need a bit of direction on).

The power supply board is L5L01F / COV33697901. When the tv gets plugged in, the power light just blinks red 3 times. If it gets fully discharged first, the screen flashes on for a second just long enough to see the LG symbol pop up and then shuts off and the power light blinks 3 times. I didn't notice any leaking/bloating on the board. I tried disconnecting the main board and powering it on but the leds don't come on at all.

I just got my first digital multi-meter yesterday. Assuming I'm using it correctly, the voltage to the main board is ~3v low supposed to be 13v according to the power supply board but reading ~10v. This seems to indicate that there might be a power issue.

Also, one of the -led prongs reads lower than the other 2 (led2- reads almost nothing compared to led1- and led3-) but I don't know what the voltage is supposed to read. This seems to indicate that there might be a bad led as well.

I've repaired electronics in the past by swapping out bad parts but this is my first time attempting work on a circuit board. Please help guide me through this. Thanks!

Last edited by slip; 10-16-2019 at 12:34 PM.. Reason: updating title and description for better clarity
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Old 10-16-2019, 02:05 PM   #2
nomoresonys
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Default Re: LG 50UH5500 need fix

Post some good clear pictures of each board and one of the whole back to see how they are connected, check number 2 and 3 in my signature for testing procedure if needed.
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1) https://www.youtube.com/watch?v=4F2J1Dkf4Is
HIGH VOLTAGE HAZARD demonstration. Video by Electronic Doberman.
2) https://www.youtube.com/watch?v=4v8DcqCNG4A
Power supply board voltage testing by shopjimmy.
BE VERY CAREFUL WITH POWERSUPPLY, VOLTAGE ON PRIMARY/HOT SIDE CAN BE DEADLY, THE CAPACITORS CAN HOLD A VERY BIG CHARGE LONG
AFTER TV HAS BEEN UNPLUGGED.
3) Test connector from mainboard to powerboard on powerboard side with all boards hooked up, 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. So we can see all the voltages and what they are doing. Try to do test just as instructed, example in link 2 if needed.

Last edited by nomoresonys; 10-16-2019 at 02:07 PM..
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Old 10-16-2019, 04:54 PM   #3
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Default Re: LG 50UH5500 need fix

here is the psu
Attached Images
File Type: jpg cov33697901.jpg (456.0 KB, 10 views)
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Old 10-16-2019, 05:14 PM   #4
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Default Re: LG 50UH5500 need fix

Picture is too blur to read anything on the board. How about the pictures of the whole top and bottom side of YOUR power board and the whole backside of the TV showing all the boards?
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Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/

TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Old 10-16-2019, 05:14 PM   #5
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Default Re: LG 50UH5500 need fix

The LG logo flash is a symptom of bad led backlights but you may have other issues with the power supply.

Last edited by neilc6; 10-16-2019 at 05:18 PM..
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Old 10-17-2019, 09:25 AM   #6
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Default Re: LG 50UH5500 need fix

Sorry for the delay. Kids got home from school so I had to put this on hold. Here's the photos of my board
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File Type: jpg 20191017_101729.jpg (1.58 MB, 6 views)
File Type: jpg 20191017_101755.jpg (1.95 MB, 4 views)
File Type: jpg 20191017_101840.jpg (1.93 MB, 6 views)
File Type: jpg 20191017_101905.jpg (1.68 MB, 3 views)
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Old 10-17-2019, 10:31 AM   #7
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Default Re: LG 50UH5500 need fix

Quote:
Originally Posted by budm View Post
Picture is too blur to read anything on the board. How about the pictures of the whole top and bottom side of YOUR power board and the whole backside of the TV showing all the boards?
Please let me know if the photos I posted today are good enough. If not, I'll take more. Thanks for helping.
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Old 10-17-2019, 10:34 AM   #8
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Default Re: LG 50UH5500 need fix

Quote:
Originally Posted by neilc6 View Post
The LG logo flash is a symptom of bad led backlights but you may have other issues with the power supply.
That's what I was thinking too. With the low voltage on LED2-, I hope I don't need to buy a whole new strip. Do you know of any good tear-down videos for this model so I can get to the led strips without messing anything up?
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Old 10-17-2019, 10:50 AM   #9
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Default Re: LG 50UH5500 need fix

Quote:
Originally Posted by nomoresonys View Post
Post some good clear pictures of each board and one of the whole back to see how they are connected, check number 2 and 3 in my signature for testing procedure if needed.
Please let me know if the photos I posted today are good enough. If not, I'll take more. Thanks for helping.
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Old 10-17-2019, 11:56 AM   #10
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Default Re: LG 50UH5500 need fix

You have 3 LED strings, LED -1, -2, -3 is the Cathode return for each LED string.
So it looks like you have open circuit in LED string #2 based on your reports.
But to really verify you need to do the test 6 times for each LED string.
Set meter to 200VDC scale. All the connectors are in place.
You will keep the black probe on the chassis, RED probe on LED 1+ then turn on the TV while watching the meter to see how high the Voltage jumps up to then wait 10 seconds to see how low it goes down too, then turn off the TV, repeat the same test on the other 5 pins of the LED connector.
https://www.shopjimmy.com/catalogsea...?q=LG+50UH5500
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Old 10-18-2019, 09:11 AM   #11
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Default Re: LG 50UH5500 need fix

Quote:
Originally Posted by budm View Post
You have 3 LED strings, LED -1, -2, -3 is the Cathode return for each LED string.
So it looks like you have open circuit in LED string #2 based on your reports.
But to really verify you need to do the test 6 times for each LED string.
Set meter to 200VDC scale. All the connectors are in place.
You will keep the black probe on the chassis, RED probe on LED 1+ then turn on the TV while watching the meter to see how high the Voltage jumps up to then wait 10 seconds to see how low it goes down too, then turn off the TV, repeat the same test on the other 5 pins of the LED connector.
https://www.shopjimmy.com/catalogsea...?q=LG+50UH5500
LED1+ = 60v
LED2+ = 60v
LED3+ = 60v
LED1- = 7v
LED2- = 0.01V
LED3- = 6.7v

There doesn't appear to be any changes in voltage.

I went to shopjimmy to get prices of LED replacements but all they have are the full strip sets. I'd rather save money on doing the replacement on the strips that are in it. Any idea which specific LED model this TV uses?

Also, the psu is still giving 3v less to the main board than it shows it should be giving. Is this a problem or is it normal?

Last edited by slip; 10-18-2019 at 09:13 AM..
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Old 10-18-2019, 09:21 AM   #12
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Default Re: LG 50UH5500 need fix

If anyone reading this thread is in need of a decent tear down video for this model TV, shopjimmy posted this in March: https://youtu.be/Un80z_fJr7s

The only thing I noticed that they didn't mention was the black film covering the boards on the bottom of the tv. I'm guessing that film is unnecessary?
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Old 10-18-2019, 10:40 AM   #13
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Default Re: LG 50UH5500 need fix

"LED2- = 0.01V" Open circuit on #2 string.
Is it worth to open up the panel again if the other 2 strings fail later?
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Old 10-18-2019, 11:53 AM   #14
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Default Re: LG 50UH5500 need fix

Quote:
Originally Posted by budm View Post
"LED2- = 0.01V" Open circuit on #2 string.
Is it worth to open up the panel again if the other 2 strings fail later?
Well, I opened it up to test the led strips. 11/12 work perfect. I tested each of the leds on the one strip that didn't light up and it turned out 5/6 of them are good too. So, 71/72 leds work fine. It seems like only one actually needs to be replaced. I think what you're saying makes sense but I'd rather just replace the one than spend more $ on replacing all of them. Aren't the leds only about $1 each?
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Old 10-18-2019, 12:04 PM   #15
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Default Re: LG 50UH5500 need fix

Your call, just be sure you set the backlights setting to as low as you can tolerate after repair so the leds last longer, on lots of tvs the default setting is max so they burn out way too soon.
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Old 10-18-2019, 12:11 PM   #16
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Default Re: LG 50UH5500 need fix

Quote:
Originally Posted by nomoresonys View Post
Your call, just be sure you set the backlights setting to as low as you can tolerate after repair so the leds last longer, on lots of tvs the default setting is max so they burn out way too soon.
Thanks for the tip! Do you know how I could find out which LED these strips have on them? They look like they might be 3030 3v but I don't want to get the wrong one by mistake.
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Old 10-18-2019, 12:13 PM   #17
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Default Re: LG 50UH5500 need fix

Whats your panel number? should be a sticker on the back metal chassis.
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Old 10-18-2019, 12:42 PM   #18
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Default Re: LG 50UH5500 need fix

Quote:
Originally Posted by nomoresonys View Post
Whats your panel number? should be a sticker on the back metal chassis.
The sticker says:

Skyworth

RDL500WY
(QD0-00B)

Rev.00

R500J1S1623A01006800
Cell: T761N243AU03
Ty: V500DJ2-QS5

RoHS
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Old 10-18-2019, 01:08 PM   #19
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Default Re: LG 50UH5500 need fix

I just ran an experiment on the bad strip. I attached a thin piece of copper wire to connect the top and bottom (+/-) of the bad led to bypass it and the rest of the strip lights up now. How bad of an idea would it be to put it back together and use it like that while I'm waiting for the replacement parts?
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Old 10-18-2019, 01:24 PM   #20
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Default Re: LG 50UH5500 need fix

Just realized one more interesting thing by accident. That bad led, it actually does light up if you apply pressure to it. Maybe it just needs to be heated and reseated? This was an unexpected turn of events. I'm still trying to wrap my head around it because for hours I knew that led didn't light up and it just did.
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