LG 42PX4RVH Picture turns green

[Engineersfoot]

Hi everyone,

I'm having an issue with an LG plasma TV. The chassis is RF-052C. Powering it from cold, after about 45 minutes the picture turns green. Sometimes the screen becomes jittery and shaky like a glitching video game before turning green. I tried both video inputs and the same thing happens on both. Currently waiting to see if the symptom is the same using over the air TV. The buttons also become unresponsive. Audio remains functioning normally throughout.

Since sometimes the buttons also stop working, I have to unplug it to power it off. Unplugging it for roughly 3-4 seconds and plugging it back in the set goes back to normal for several minutes before failing again. When I'm able to use the buttons and I power it on and off from there the fault also goes away for a while. This even if the set is only off for a very brief moment.

Attached are some pictures of the fault and how it looks on screen as well as a service manual:

Service Manual

https://www.sendspace.com/file/so2imj

I'm experienced in electronics but not very used to diagnosing plasma TVs.

First picture is the green screen issue and the second is the screen while it jitters and glitches.

[Engineersfoot]

Re: LG 42PX4RVH Picture turns green

Anyone?

[martino]

Re: LG 42PX4RVH Picture turns green

Can you post pictures of the boards?
It seems to me it's temperature related,what you could do is take a hair dryer and heat up one board at the time to see if you can speed up the fault...
I would almost start doing that with the mainboard...Once you found the "heat sensitive" area,take a can of air(those air cleaning cans for computers)HOLD IT UPSIDE DOWN,and spray the suspect area(it will freeze the area)...
With fiddling between heat and freezing,you should be able to pin point it down to a fairly small area,then it's time to check that area for either a cracked solder joined or a heat sensitive component,a BGA chip,smd cap/resistor....
You can also try,once found the area,to take a plastic or wooden object and gently press on that area to see if you get a reaction...Don't push to hard as you may short out the board against the chassis....wiggling connectors in the area might also yield a result...

[Engineersfoot]

Re: LG 42PX4RVH Picture turns green

Okay I went around heating the individual boards for a couple minutes but it didn't do anything. I focused on the main board but I heated all of them for at least 2 minutes or so. Was afraid to keep going any longer in case it caused some damage, hair drier is pretty hot.

I'm currently waiting for the fault to repeat. Once it does I'll prod around to see if movement causes any change. Keep in mind that the fault goes away for up to 30 minutes simply by turning the set off and back on immediately which means it's not having much time to cool.

Here is the picture of the back as you requested. If you need close ups let me know.

[selldoor]

Re: LG 42PX4RVH Picture turns green

A quick easy test is (after the set has been off for 15 minutes ) unplug clean and reseat ALL cables that you can see are removable. One hard to spot might be from the main board to the Tcon

[martino]

Re: LG 42PX4RVH Picture turns green

Is there a board hidden behind the mainboard? I had the same thing once where it was not responding to heat even though I knew it was heat sensitive.
Found the logic board hiden behind the mainboard, even with hair dryer on an angle pointed at the cavitie where board sat didn't do anything. I then moved the mainboard off to the side so I could aim directly at the board behind it and had a reaction within 10 seconds.

[Engineersfoot]

Re: LG 42PX4RVH Picture turns green

I actually reseated all the connectors on the main board yesterday. Will try doing all the ones I can find next. I don't think there's any board hiding behind the main board. I'll remove the main board to make sure, but I don't see any on the service manual either.

Today the fault behaved a little bit differently. No glitching phase this time. And it took over 2 hours for the green screen fault to appear. As usual turning the tv on and off rapidly fixed the fault and 35 minutes later I'm still waiting for the fault to reoccur.

While the fault was present I tried tapping around the different boards with no difference.

Before the fault occurred I also discovered a couple of details I hadn't noticed before. When the signal source is on video input 1 the image starts to become dim. There are noticeable steps as it looses brightness, roughly one step per second. Never goes completely dark, just becomes somewhat dim. Flipping through signal sources and returning to video 1 resets the brightness and you can observe it going back down right afterward. The same seems to occur on video input 2 but it's a lot more subtle and takes a longer time to become noticeably dim. Again flipping through the signal sources and returning to video 2 resets the brightness to normal. On screen display seems unnaffected by this and in fact opening the menu seems to reset the brightness as well.

The other thing I noticed is that when the screen goes from displaying something to suddenly going to a black screen, there are a few tiny sparkles left behind. For example when the on screen display on the upper right corner is displaying the selected signal source and the background is completely black, once the on screen display disappears it leaves a square outline of sparkles where the on screen display was. Not sure if that is normal, this too was before the green screen fault occurred. The sparkles aren't very bright or noticeable but they're there.

I decided I'd take some close ups and some more pictures to show the details of the "green screen fault" fault.

The pictures are in the following order. Signal source is a DVD player playing a CD.

1. Close up of the upper left hand corner while the green screen fault is present.
2. Close up of the signal source being displayed along with the on screen display indicating signal source.
3. Close up of the TV displaying over the air static along with the on screen display.
4. Close up of the on screen display while there is no signal source present.