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Old 01-31-2022, 05:36 PM   #1
Storyteller12
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Default LG 70UH6350 Mainboard issue

Got this tv and tracked down the problem to the mainboard. Tv standby light shows the tv turns On but no picture or backlights. Tested backlights with backlight tester and all is working well. Also I put in another mainboard to verify and backlights turn on fine.

Anyways I cannot find another mainboard for this TV. So Iím trying to fix the board. Any suggestions on where to start?
Could it be the eeprom possibly?

I donít work on many lg TVs and usually when I do itís the backlights.

Thanks Iím advance

Pics attached with heat sink and with it removed.
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Old 01-31-2022, 05:56 PM   #2
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Default Re: LG 70UH6350 Mainboard issue

yours ways to take the point the MB working regard front indicatores or BL are absoult wrong.. sorry
with original MB did you have the optical audio port lit on RED ??
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Old 01-31-2022, 06:15 PM   #3
Storyteller12
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Default Re: LG 70UH6350 Mainboard issue

Hi Diah, No optical audio did not show red
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Old 01-31-2022, 06:24 PM   #4
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Default Re: LG 70UH6350 Mainboard issue

so it didn't turn on at all.. do you have after turn on 12V and 24V on the MB socket which it come from PCB?
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Old 01-31-2022, 06:27 PM   #5
Storyteller12
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Default Re: LG 70UH6350 Mainboard issue

Yes the red optical did not turn on at all. All voltages match what’s on the legend. Except all 24v measure 26v. But that should not matter as the 2nd main board I used to test with worked fine.
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Old 01-31-2022, 06:30 PM   #6
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Default Re: LG 70UH6350 Mainboard issue

we are talking on original MB. not the test one.. 24 rail go to 26 mean you have at audio section issue or one of HDMI USB issue
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Old 01-31-2022, 06:34 PM   #7
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Default Re: LG 70UH6350 Mainboard issue

I understand we are talking original board. The 26v is the same when mainboard disconnected from power supply. So would that rule out the audio or usb and hdmi?
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Old 01-31-2022, 06:38 PM   #8
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Default Re: LG 70UH6350 Mainboard issue

no but this not normal what you are measuring. 2 v more on 24 rail will toast much parts on the section's i mentioned as 12 rail due to panel vcc
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Old 01-31-2022, 06:42 PM   #9
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Default Re: LG 70UH6350 Mainboard issue

can we see the power boards and the print label charts of its dc supply
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Old 01-31-2022, 06:45 PM   #10
Storyteller12
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Default Re: LG 70UH6350 Mainboard issue

All 12v on the legend measure 12v and so does the tcon when I checked that. It’s just the 24v that measure 26v. Not sure though cause everything is normal with 2nd mainboard.

So assuming it’s the mainboard anything specifically I can check?
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Old 01-31-2022, 06:49 PM   #11
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Default Re: LG 70UH6350 Mainboard issue

MAn... you tested main boards with fault on PCB was there 24V are 26V. ( its short time to toast ) the original one which suffer from the PCB toasted already.. need first to bring this 24V rail to normal then working on the Original MB.
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I understand we are talking original board. The 26v is the same when mainboard disconnected from power supply. So would that rule out the audio or usb and hdmi?

Last edited by Diah; 01-31-2022 at 06:55 PM..
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Old 01-31-2022, 06:57 PM   #12
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Default Re: LG 70UH6350 Mainboard issue

I’ll double check tomorrow about the 26v when disconnected from power supply. Maybe I’m wrong and that’s why the 2nd board worked fine.

That’s for the help. I’ll report back tomorrow after I confirm
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Old 01-31-2022, 11:05 PM   #13
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Default Re: LG 70UH6350 Mainboard issue

Did you get your 12v to panel?
Things you need on most mainboards. 5v, 3.3v, 1.8v, 1.2v, clock pulse
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Old 02-01-2022, 08:42 AM   #14
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Default Re: LG 70UH6350 Mainboard issue

I got 12v on the tcon. Not sure about the panel as I have not hooked it up.
Every lg tv I’ve had needed the backlights replaced so I just assumed and removed panel.

To my surprise all leds tested good. So I have been troubleshooting with the panel removed for the time being.

Will update later on the 26v after I get to the office and test
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Old 02-01-2022, 11:46 AM   #15
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Default Re: LG 70UH6350 Mainboard issue

Update. I made a mistake There is no power on the 24v pins with mainboard disconnected.
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Old 02-01-2022, 11:54 AM   #16
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Default Re: LG 70UH6350 Mainboard issue

Quote:
Originally Posted by Storyteller12 View Post
Update. I made a mistake There is no power on the 24v pins with mainboard disconnected.
do you mean you run the PCB standalone with jumpers as mainboards disconnected from PCB so no 24V.. !!!
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Old 02-01-2022, 11:55 AM   #17
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Default Re: LG 70UH6350 Mainboard issue

I did some testing on the main board and found a lot of shorted caps. Iíve marked them and uploaded a phot of it. Also I found an 8 pin ic I cannot find a data sheet for that is shorted to ground on 5 of the 8 pins.

Itís ic101 and labeled with marking 4G25 60473

Iím thinking that may be the problem but not sure.

Any further help is appreciated
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Old 02-01-2022, 11:55 AM   #18
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Default Re: LG 70UH6350 Mainboard issue

There wouldn't be would there, without the mainboard telling the powerboard to turn on?
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Old 02-01-2022, 11:58 AM   #19
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Default Re: LG 70UH6350 Mainboard issue

If you still have both mainboards, you can compare the readings to each other.
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Old 02-01-2022, 12:10 PM   #20
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Default Re: LG 70UH6350 Mainboard issue

So what voltages have you found?
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