LG 55LM620T-ZE Not turning on

[NormanBates]

Hello everyone. The tv wont turn on. It got a red standby light that blinks as when pushing power on button. The tv has been laying for about 1 year now but what happened was that i was plugging i an antennea cable or maybe vga(cant remember which one it was ) and it just died instantly. Attaching pictures of the tv and the boards. I alson took some voltage readings as in one of the attached images. Someone who can point me in the right direction on repairing it? And btw, the readings i got was when plugging the powercord in and measured it in standby mode.

[attainteddragon]

Re: LG 55LM620T-ZE Not turning on

do you have a couple of 1k resistors to jump the ps on?

[NormanBates]

Re: LG 55LM620T-ZE Not turning on

do you have a couple of 1k resistors to jump the ps on?

Dont really have any components laying around. But if needed for testing i could buy a few.

[dick_barton]

Re: LG 55LM620T-ZE Not turning on

All the secondary voltages appear to be up and running but you don't give the voltages for DRV_ON or ERROR.

[NormanBates]

Re: LG 55LM620T-ZE Not turning on

I saw now in my first that i wrote what could be misunderstood. To clarify, when I plug the cord in the red light goes on and stays like that until i press the power button, then it starts blinking and keeps doing that for a while before it goeas back to a static light. Some additional info is that i have a green led on the powerboard that after the tvhave been connected for about 30 secs start to blink. Blinks 5 times pauses and then 5 times again and keeps going like that.

[NormanBates]

Re: LG 55LM620T-ZE Not turning on

All the secondary voltages appear to be up and running but you don't give the voltages for DRV_ON or ERROR.

Everything that is left out in the "measuring" picture i have a 0V on.

[Andrew F. Ali]

Re: LG 55LM620T-ZE Not turning on

I noticed that on the pin labelled N.C (Not Connected) you have 12V. That is not right. I think there is an error in your readings Perhaps you could label the pins as pin1 ERR 12 V, pin 2 PS-ON 3.5V just as an example.

[dick_barton]

Re: LG 55LM620T-ZE Not turning on

DRV_ON is missing and should be around 3V to activate the backlight led circuitry. It's a signal from the mainboard so you may have a led fault giving an Error response turning off the DRV_ON signal.

Can you check what voltage is at PWR_ON when in standby and when you switch it out of standby. Some PWR_ON need to the voltage on the pin to go low to come out of standby and some need to go high to come out of standby.

[NormanBates]

Re: LG 55LM620T-ZE Not turning on

I noticed that on the pin labelled N.C (Not Connected) you have 12V. That is not right. I think there is an error in your readings Perhaps you could label the pins as pin1 ERR 12 V, pin 2 PS-ON 3.5V just as an example.

On the N.C pin i have nothing. The text inside the box labeled CONNECTOR is taken from board. To the left inside the box there are (at least how I think it is) the suggested values for the left column of pins and the ones to the right are for the right column of pins. The numbers underthe label READINGS are my measurements of respective pin in each column.

[NormanBates]

Re: LG 55LM620T-ZE Not turning on

DRV_ON is missing and should be around 3V to activate the backlight led circuitry. It's a signal from the mainboard so you may have a led fault giving an Error response turning off the DRV_ON signal.

Can you check what voltage is at PWR_ON when in standby and when you switch it out of standby. Some PWR_ON need to the voltage on the pin to go low to come out of standby and some need to go high to come out of standby.

In standby mode i have 0,98V and when pushing power-on button it goes down to 0,8V for a few seconds, then back to 0,97 and then again back down and keeps doing that e few times.

[attainteddragon]

Re: LG 55LM620T-ZE Not turning on

can you disconnect the loom that goes from the p/s to the main and measure what the ps/on pin reads. this will let us know if it requires a high or low voltage control to turn on.
your current measurement is what i would call neither, so need to confirm this.

[budm]

Re: LG 55LM620T-ZE Not turning on

https://www.badcaps.net/forum/attach...9&d=1530363633
Based on what you show, the PWR_ON is fine otherwise not ALL the switched power supplies will be putting out. You can easily verify if the PWR_ON is OK or not by checking the DCV right between the two legs of the main filter cap, if you have close to 400VDC then the PWR_ON signal is OK otherwise you will not have PFC Boosted Voltage on the main filter cap. The PWR_ON may be stuck ON at this point if it does not toggle to 0V (= off). Some power supply boards do use <1V = ON, 0V = OFF instead of typical 2 ~5 V = ON, <1V = OFF.
You do not have Dimming control on one of the pin but not at the other P-DIM pin? Backlights ON signal is not present.

[NormanBates]

Re: LG 55LM620T-ZE Not turning on

can you disconnect the loom that goes from the p/s to the main and measure what the ps/on pin reads. this will let us know if it requires a high or low voltage control to turn on.
your current measurement is what i would call neither, so need to confirm this.

Do you mean the connector that i measured on on so far(P201)? If so it gives me 0V when disconnected.

[NormanBates]

Re: LG 55LM620T-ZE Not turning on

https://www.badcaps.net/forum/attach...9&d=1530363633
Based on what you show, the PWR_ON is fine otherwise not ALL the switched power supplies will be putting out. You can easily verify if the PWR_ON is OK or not by checking the DCV right between the two legs of the main filter cap, if you have close to 400VDC then the PWR_ON signal is OK otherwise you will not have PFC Boosted Voltage on the main filter cap. The PWR_ON may be stuck ON at this point if it does not toggle to 0V (= off). Some power supply boards do use <1V = ON, 0V = OFF instead of typical 2 ~5 V = ON, <1V = OFF.
You do not have Dimming control on one of the pin but not at the other P-DIM pin? Backlights ON signal is not present.

Main filter cap? Is that the 2 big ones on the board? I have 400V on them as soon as i plug in the cord.

[attainteddragon]

Re: LG 55LM620T-ZE Not turning on

disconnect the main from the p/s and check them again.

[NormanBates]

Re: LG 55LM620T-ZE Not turning on

disconnect the main from the p/s and check them again.

All i have when disconncted is the 3,63V, all the others are 0V.

[dick_barton]

Re: LG 55LM620T-ZE Not turning on

Place your probes across either of the two large capacitors with 450V written on them. Do not let the meter probes slip.

[NormanBates]

Re: LG 55LM620T-ZE Not turning on

Place your probes across either of the two large capacitors with 450V written on them. Do not let the meter probes slip.

With the connector (P201) disconnected i get 328V and when connected i get 400V.

[attainteddragon]

Re: LG 55LM620T-ZE Not turning on

ok, so your main is stuck on. i'm not sure if you can get an eeprom for this board, or you would be looking at a replacement.

[NormanBates]

Re: LG 55LM620T-ZE Not turning on

ok, so your main is stuck on. i'm not sure if you can get an eeprom for this board, or you would be looking at a replacement.

So getting a new mainboard (and just to be sure, that is the one to the right in the photos of my tv?) would probably be easiest soultion?