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TV stopped powering on

My TV stopped powering on. It is a LG LED, Model: 55LV5400-UB. In the middle of a heat wave, I tried to make volume louder, there was a click and it turned off. Reset by unplugging failed, as did trying to force a reset by holding a power button. Normally, after pushing the power button: a red light would come on, fade out, be replaced by white, fade out and start to work. When turning off: a white light would come on, fade out and then TV would turn off. Now, after pushing the power button: a red light comes on, fades, is replaced by white, which fades, then white comes on again and fades without any image appearing. IE according to indicators: TV starts to power on and then immediately shuts down. The TV is about 10 years old but all capacitors on the power board look fine. The next step in diagnostics is to check output voltages on the power board but I have the following questions:

1. LG tech advice given for a similar TV (https://www.justanswer.com/tv-repair/7h2...) says to test outputs 'with NOTHING connected to the Power supply but AC power, the Main-board, and the little board that houses the Power Switch.' Mine doesn't have a connection from the power-board to the power switch board but does that mean I have to disconnect power supply board's ribbons on LED connectors and maybe something going from the main-board? [Also, this problem was resolved by replacing a main-board (not power-board)]

2. I can't seem to disconnect connectors with ribbon cables. LG uses some kind of a snap lock which I can't figure out and I don't want to break a connector. If there is a method to disconnecting them please share it.

3. The power board connector going to the main-board has 24 pins but not all pins are labeled with voltage numbers so how do I confirm what are the proper voltages on them? (Further, to access all 24 pins I need to disconnect yet another ribbon connector which I can't figure out...).

4. Finally, given that comments given here for a similar make and model:

My LG TV 55lv5500 suddenly turn black with no sound or picture.

confirm that the problem was resolved for several people with same or similar TV's not by replacing the power board but by re-flowing the chip on the main-board, should I even bother testing the output voltages or go straight into re-flowing?

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@tronz yes you do want to go ahead and measure the voltages. Also post some good pictures of your board with your QUESTION. That way we can see what you see. Going by your description I would focus on the power board at this time. Just to verify, you did say you already replaced the main board. Reflow may not what your TV needs. You should go ahead and do some more troubleshooting. First step I suggest is that you check the standby voltage on your board. You should have something like 3.5-5 V on it. Check PS-ON (pin 1 on P201) when you push the power button. Does the voltage go up and stays there or does it drop after a few second. That would mean an error has been sensed. If your power board is a LG EAY62169901 turn it over. Your voltages etc. are listed on P201.

3.5V_ST (3.55V) output P201 pins 9~12

12V output P201 pins 17, 19 and 21

24V output P201 pins 2, 3 and 4.

Not sure about the connectors that you are describing as tough to remove. LG connectors commonly have tabs on either side that need to be depressed to remove the cable.

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Adding images to an existing question

Update (07/09/2021)

Here is the

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troubleshooting chart for your TV.

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53 Comments:

Thank you for a quick response. Just uploaded pictures:

Regarding 'Just to verify, you did say you already replaced the main board.' - NO, you must be confusing me with someone else.

Regarding voltages: please look at pic: PBvoltOut.jpg

Regarding connectors: squeezing the tabs towards the center of the connector does not seem to allow it to be pulled out

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@tronz Sorry and I guess I assumed that you had replaced the main board based on this " [Also, this problem was resolved by replacing a main-board (not power-board)]" I guess that was actually a reference to the question from "Justanswers.com" and not your TV.

Yes, those are typical LG connector and a pain since they are really tight. You are right that you have to squeeze them together and then pull.

Once you post your images they get renamed so I cannot determine which one is PBvoltOut.jpg

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All right, lets take it one thing at a time. I just inserted a link in my first question (this site wouldn't let me do it from the start). Please re-read it and tell me what you think about that?

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The image I referred to is now 3rd from the top. It is a table for voltages on the P201 connector. To get image name for any image here, do a mouseover the image, you'll get a 3 item menu, the right one "i" will let you view Metadata. Click on that, scroll to the bottom of the list and you will see that this image name is: PBvoltOut.jpg

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@tronz yes I know which image. Did you measure those voltages as I pointed out in my answer? You should at least have the stby voltage since your get the power LED to light up. Check pin 1 and see if the voltage stays hi or if it goes lo. If it does go low than it shuts down because of a fault during POST.

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