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Old 05-19-2020, 10:01 PM   #1
kent_323is
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Default LG 65UH5500 flashes on and shuts right off

Hi,
I have the LG 65UH55 tv and it has some issues.
Right now it will not come on and stay on. Doing some reading and research on it, it could be the power supply board, LED backlights or main board.

Here's what it does:
1. plug into wall, and the red status light comes on.
2. press power button, and it will very briefly flash up the LG icon on the screen and appears to come on.. but then quickly shuts back down again and the red light comes on again.
3. press power button again, and the red light goes out, and the red light on the main board will light up briefly and go back off while the red light on the power button stays off. Screen and backlight LEDs stays off.
4. Press power button again and main power board will light its red light again and the power button will flash its red light again, and then go off.
Unplugging it from power will then allow you to start at #1 again.

I opened up the back, and I have measured the voltage at the pins on CN2 on the power supply board.
PSON pin is 3.5 and red light is on
13.5v pins are reading 8.6v
80v pins are reading 57v

Does this indicate that the power supply board is bad? I have visually looked at all of the large capacitors, and they seem fine, none of them are bulged.
What else should I check and measure?

Thanks
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Old 05-19-2020, 10:41 PM   #2
neilc6
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Default Re: LG 65UH5500 flashes on and shuts right off

Coincidence someone just messaged me with the same model with the symptom of a quick flash of the LG logo and front red LED flashing. The LG logo flash is a symptom of bad backlights and the protection circuit kicking in and shutting them down. Was a bit unsure since LGs typically stay on with the backlight shut down but I guess not in this model.

https://www.shopjimmy.com/lg-5835-w6...-strips-24.htm

Read the second review. Very difficult repair on a 65" TV with a high chance of cracking the screen since you need to remove the screen to get at the LEDs. Not sure how Shopjimmy rates the skill level as easy. Maybe on a 32" TV.

Last edited by neilc6; 05-19-2020 at 10:50 PM..
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Old 05-20-2020, 08:47 AM   #3
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Default Re: LG 65UH5500 flashes on and shuts right off

Can confirm symptoms with exact model I just repaired. One led open.

If you do the repair I would suggest a hardware mod to the led driver to reduce current to the backlight strings. Can help you with that when you get to that point.

57v sounds about right. You need to check those voltages when you power up the set to see how high they spike on each string (six strings) to determine if you have an open led in one of the strings.
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Old 05-20-2020, 09:29 AM   #4
kent_323is
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Default Re: LG 65UH5500 flashes on and shuts right off

So test the voltage on each pin that's listed as 80v on the power supply board?
If an LED string is out, what would it show as voltage?

Is there anyway to unhook the LED strips and verify that the rest of the TV is working okay?

Thanks for the help so far, I did go look at the link for the LED strips, and that seems like my same issue as well.
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Old 05-20-2020, 09:50 AM   #5
kent_323is
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Default Re: LG 65UH5500 flashes on and shuts right off

I measured the output voltages on the 80v pins.
In general for all 5 of them: 70v in standby mode, spikes to 97v when first turning on, and then goes right back down to 65v.

What does that mean?

Thanks
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Old 05-21-2020, 08:43 AM   #6
mmartell
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Default Re: LG 65UH5500 flashes on and shuts right off

Was that with the led connector plugged in ? If you're getting identical readings on all six pins then you may have a different problem.

Wait, five pins ? You should have six, there are six strings !
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Old 05-21-2020, 08:55 AM   #7
mmartell
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Default Re: LG 65UH5500 flashes on and shuts right off

So I looked up a photo of the board we're discussing and I can see now you're testing the voltages at CN401 when you should be testing them at the LED connector, CN403.

Try again with connector plugged in. Red lead to LED1+, black lead to chassis ground and turn on tv. Note the voltage. Lather rinse repeat for all six positive pins.

The set must be in the state where the screen flashes each time you make the measurement so you may have to uplug/replug each time.
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Old 05-21-2020, 09:02 AM   #8
kent_323is
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Default Re: LG 65UH5500 flashes on and shuts right off

Ok, thanks for the clarification. I will re-test and post the results.
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Old 05-22-2020, 10:05 PM   #9
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Default Re: LG 65UH5500 flashes on and shuts right off

I ended up taking it all the way apart, and sure enough, there was a Single bad LED! So I guess next step is ordering new LED strips. I'm going to replace all of them, as it isn't worth doing all this work for a single LED, and then have the next one go out next week or something stupid.
I did find this video on youtube that was super helpful in taking it apart.
https://www.youtube.com/watch?v=5ir7...ature=youtu.be

Thanks for the guidance that it was likely the LED strips.
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Old 05-23-2020, 05:47 PM   #10
mmartell
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Default Re: LG 65UH5500 flashes on and shuts right off

Very good if you'd like to do the current limiting mod in the meantime just let me know.
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Old 05-23-2020, 08:56 PM   #11
kent_323is
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Default Re: LG 65UH5500 flashes on and shuts right off

mmartell,
Yes, what does the current limiting mod entail?
Thanks
Kent
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Old 05-23-2020, 09:20 PM   #12
mmartell
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Default Re: LG 65UH5500 flashes on and shuts right off

Remove the led driver board and on the backside remove ONE of the group of three 4.3ohm resistors at location R415a, R417a, R419a, R421a, R423a and R425a for a total of six resistors - one for each led string.

The current to the leds will be reduced by about 30% if I remember correctly. I did not notice much if any change in brightness as a result. YMMV.

Picture courtesy of Shopjimmy.
Attached Images
File Type: jpg shopjimmy-cov33699501-bottom.jpg (789.9 KB, 15 views)
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Old 05-30-2020, 10:03 PM   #13
kent_323is
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Default Re: LG 65UH5500 flashes on and shuts right off

So I finally got the new LED strips from ShopJimmy, and while the part number is almost exactly the same (only the LED number is different), the PCB is NOT drilled with the same locations of the holes, so they don't fit at all!
Also, there is no adhesive on them as claimed by the description from Shop Jimmy.

Old one is 5835-W65002-LR40
New one is 5835-W65002-0P40

The hole spacing is just a little bit off, so if one hole lines up, then the other 2 do not.

Anybody else encounter this?

Now what?

Thanks
Kent
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Old 05-31-2020, 05:01 AM   #14
nomoresonys
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Default Re: LG 65UH5500 flashes on and shuts right off

Call shop jimmy, describe it just like you did here, ask m whats up with no double sided tape, they usually make things right when they make a mistake.
__________________
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.
Donations accepted with a smile and a Thank you

Last edited by nomoresonys; 05-31-2020 at 05:06 AM..
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Old 05-31-2020, 05:09 AM   #15
nomoresonys
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Default Re: LG 65UH5500 flashes on and shuts right off

I mean ffs, when you pay 100 bucks for backlights, you should at least get what you ordered, right?: https://www.shopjimmy.com/lg-5835-w6...-strips-24.htm
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Old 05-31-2020, 02:45 PM   #16
kent_323is
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Default Re: LG 65UH5500 flashes on and shuts right off

Right, you'd expect them to drop in and work.
I did send a message to ShopJimmy and replied to their auto reply with the pictures showing the differences.
Their website shows that they are not taking calls right now.... Hopefully they reply right away on Monday morning.
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Old 05-31-2020, 04:42 PM   #17
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Default Re: LG 65UH5500 flashes on and shuts right off

Wow that's BS, they have time to take your order and your money but not your call.
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Old 05-31-2020, 05:10 PM   #18
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Default Re: LG 65UH5500 flashes on and shuts right off

Welcome to the world of Coronavirus
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Old 06-01-2020, 03:03 PM   #19
nomoresonys
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Default Re: LG 65UH5500 flashes on and shuts right off

I think sj thinks they are amazon or some company...too big to be bothered with phone calls, that's a poor example tho because amazon does take phone calls, I remember a few years ago sj even helped out those that commented on their youtube videos asking for help. Now they say they just can't be bothered to help out. They have a 6 month guarantee but I get most parts for a third of their prices.
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Old 06-01-2020, 11:12 PM   #20
kent_323is
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Default Re: LG 65UH5500 flashes on and shuts right off

Well, Shop Jimmy did reply to my message right away, even got a reply Sunday night that they were working on it. This morning (Monday) the gal asked for some additional information, and then got right back to me before lunchtime.

Turns out there are actually 2 kinds of LED strips that go into this TV.
16 of strip A and 8 of strip B.
I had unfortunately only taken one strip out of the packaging, and was comparing a B style strip to an A strip location. Doh!

So once that was figured out, everything lined up perfectly.

I also asked her about the adhesive, and turns out that was a mistake in their description, as these strips for this TV don't need adhesive due to the number of screws that attach them. They were going to update the description to be correct.
So Shop Jimmy did do some good customer service, and my issue was resolved.

So a few hours later I got all of the LED strips changed out, and the rest of the TV put back together!

And by golly the dang thing even works! I actually got to watch one of my shows!

Thanks guys!
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