LG 50PN4500-UA plasma TV no picture

[Wes1835]

Hi,
I have an LG 50pa4500 plasma TV where the screen will not power on. (No picture or glow at all)

The red standby led light is on, when power is pressed it flashes three times (two times fast, delay then another flash), sound comes on and remains on for about one minute, then sound off (white noise only-no source hooked up). Red optical cable led on main input signal board is on.

When i look at voltages on power supply all of the proper voltages look to be correct according to markings on PC board, including the Va@55v and Vs@205v (matches voltages on label). Note: no clicking or sound when turning on - don't know if there is a relay on this model or not.

Voltages appear to be present on the ZSUS and YSUS boards, and I cannot find any blown fuse or other visual issue on these boards.

Looking for help in identifying next logical steps to make to troubleshoot problem. Appreciate any help. Thanks. Wes

[Wes1835]

Re: LG 50PN4500-UA plasma TV no picture

Verified all outputs from power supply good and stable. There is no relay on this power supply so no clicking.....Verified voltages on Ymain board (looks like this model combined YSUS and buffer boards into one) and Z - all match that required per the plasma display sticker. Still no flash on led control board....going there next. Any help or suggestions would be appreciated.

[ploof]

Re: LG 50PN4500-UA plasma TV no picture

did you ever find the problem?

[Dcal]

Re: LG 50PN4500-UA plasma TV no picture

Having same issue any ideas or troubleshooting would be appreciated.

[Hamie]

Re: LG 50PN4500-UA plasma TV no picture

You upload a picture of your y-sustain.

Can you tell me the following.

Is there a green led on the control board?
Is the z-bias voltage 70v when it should be 140?
Is the -VY voltage 10-20v?

[Dcal]

Re: LG 50PN4500-UA plasma TV no picture

Ok so taking apart the y-sustain board I discovered a melted component at C417 location that I believe is the problem.

[Dcal]

Re: LG 50PN4500-UA plasma TV no picture

I guess my question now would be what is that and where do I get it?

[phillipmulvaney]

Re: LG 50PN4500-UA plasma TV no picture

I believe I may be having the same problem with my LG as well. I opened the back and read where DCAL had the melted component at C-417. Mine was a melted component at C-413. I do have a green LED on the control board. I have nothing on the z-biaz voltage and I have 19.5 vy voltage.

The VA I have 55 volts, I have 205 at the vs. Any thoughts? Any help would be appreciated.

[Alastair E]

Re: LG 50PN4500-UA plasma TV no picture

you'll need to check the dc-dc converter stage that derives the VZ-Bias and the -Vy--Check both these lines for shorts/low resistances

I suspect--because I cannot see in those pics (they will not enlarge, only thumbs) that the suspected 'melt' is just glue applied during manufacture, and not in any way connected to the fault.

[phillipmulvaney]

Re: LG 50PN4500-UA plasma TV no picture

Alastair E......... I will attach a picture of where my C-413 looks to be burned. As I had mentioned, I believe I am having the same problems.

[ReeceyBurger123]

Re: LG 50PN4500-UA plasma TV no picture

Yeah thats toast ! This means that you probably have some shorted Igbts which is fun.... You have a Dmm and know how to check for S/C ?

[ReeceyBurger123]

Re: LG 50PN4500-UA plasma TV no picture

This set also chains the ERC ciruit meaning that a bad Ysus can kill the Zsus so if you decide to replace/repair one you will need to do the other if not you will be back at step one.

[Dcal]

Re: LG 50PN4500-UA plasma TV no picture

Thanks for the update guys. Mine looks exactly like phillipmulvaney. Any ideas what causes this? And ReeceyBurger123 how certain are you that the zsus would be damaged? If so how would I test it?

[phillipmulvaney]

Re: LG 50PN4500-UA plasma TV no picture

Thank you for the information ReeceBurger123. I do have a DMM however I don't know exactly where to start searching for the S/C. Do you have any information on how I would begin?

Thank you.

[ReeceyBurger123]

Re: LG 50PN4500-UA plasma TV no picture

Ok does your meter have a diode mode, if so put it on to it and short the leads together does it beep or what reading does it show on the display ? This reading is similar when testing components if a device is shorted the meter will act like it does when you short the leads together. Do you understand ?

[phillipmulvaney]

Re: LG 50PN4500-UA plasma TV no picture

I know how to use the dmm, I just don't know if there is a specific process I should use to in order to find the s/c. I don't understand the flow. Is there a specific thing that I need to do to find where this board is s/c at?

[phillipmulvaney]

Re: LG 50PN4500-UA plasma TV no picture

I am getting ready to remove the ysus board and I am wondering how you remove the ribbons from the ysus board? The ribbon coming from the control board the release is towards the ribbon, easy to do. The release from the ribbons to the ysus board (6 of them) the release is opposite of the ribbon. I cant remove them.

[Logen1]

Re: LG 50PN4500-UA plasma TV no picture

Philipmulvaney. Did you ever end up fixing this tv?

[Logen1]

Re: LG 50PN4500-UA plasma TV no picture

I have this same problem. Tv turns on and stays on just fine I can't here anything when I adjust volume and there is no green led flashing on my logic board. Dies anyone have any idea where I should start? Any an all advice would be greatly appreciated.