LG PLASMA 50PQ30 rainbow effect + dark screen

[Cnypitbulls]

I kno I've seen a few threads on here but I just wanted first hand feed back from the experts or anyone who also encountered this problem. First off I bought this tv used with this existing problem the screen when tv is on shows a darker than usual picture then there is some type of rainbow inverted effect, don't know if that would describe it. I have a video I just put up on YouTube so you guys can see what I'm talking about.... Im thinking its the y-sus then I think it's the z-sus, not really sure because I'm no expert. I've fixed some lcd tvs that's why I bought this cheap thinking I can fix it.... Please help people... Here is the link to the YouTube video

http://m.youtube.com/watch?v=NKupTBP9WWg

Also when I first got the tv there was a lot of moving red dots on the screen so I opened up the back and tweaked with those Philips head knobs and that reduced them a little bit

[tom66]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

It is likely control board or main board, not y-sus/z-sus fault.

[Tvbob]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

Check the caps in the power supply, also the decoupler caps around the regulators on the main video board. A can of freeze spray may help.

[Cnypitbulls]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

Thanks tom66, so it's likely the control board or the main board, any idea which one would most likely be the culprit? tvbob thanks for your input but am not that advanced in repair usually I just buy and replace a board if I know it's defective.. I took some pictures of the control board and of the main board the main board looks like sum of the plastic on there was melting due to heat not sure if it might be the culprit any more input is well appreciated!

[tom66]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

There are two points marked EXT AUTO GEN on most LG plasma control boards. Unplug the LVDS cable between the main and control boards and jumper EXT AUTO GEN with a piece of wire. When the TV is turned on test patterns should appear. There should be some smooth gradients there, if there are then post a picture so we can see what they look like.

e.g. here is older 42V7 panel https://www.youtube.com/watch?v=soZ9jblKBpE (but with panel fault leading to sparkling pixels/poor white tones)

[Cnypitbulls]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

Ok I did that and made a video of it..

Here's the video

http://m.youtube.com/watch?v=KOqGm_z0eLs

[tom66]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

Your control board is the fault then, as the gradients should appear smooth but they do not.

[Cnypitbulls]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

Thanks tom66, just ordered one off the net, will update you guys when the replacement is made! If I don't update you guys then that just means tom66 was right and no need for me to come back to this thread lol

Will update you guys anyway!

[tom66]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

Please do -- it means others can benefit from your experience and we can keep more TVs out of the trash!

[Cnypitbulls]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

OK I replaced the logic board but still no difference. Also tried the self test mode using the EXT AUTO GEN on the control board and the gradient still looked the same as before.

[Cnypitbulls]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

ttt

[tom66]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

That's strange. Did you match the logic board panel model to the sticker? (e.g. panel shows PDP50T1#####, install a logic board from a 50T1 panel.)

[Cnypitbulls]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

To tell you the truth to picture got a tiny bit better but the posterization is still there along with the darker than usual display. Yea I matched it up to the sticker.

[tom66]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

Can you perhaps make the same video with the new board so the improvement is visible?
Where did you order your board from?

[Cnypitbulls]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

The improvements are very very minor, probably only see able by my eyes lol

Here is a link to the video
http://m.youtube.com/watch?v=65ClhtAoias

Ordered the board from eBay repair shop

[Cnypitbulls]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

Ttt

[tom66]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

I'm not certain. In the EXT AUTO GEN tests, the main board was completely disconnected, except for power? Therefore, the only problem can be on the control board or driver boards. A driver board failure should only lead to regional faults though (i.e. half or a 2-3 inch portion of the screen.) Can you try reseating all the cables going from the control board to the bottom of the plasma panel?

[Cnypitbulls]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

Correct, it was disconnected except for the power. I took all cables off periodically b4 a few times and still had the same problem. Would the control or the main board also affect the darkness issue? There is also another issue I didn't mention, when the tv is first powered on I get like a blue flash that's bright then it fades away real quick, don't know if that would help diagnose the issue!

[tom66]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

I think the blue flash is normal on these panels, it is due to how the screen is initialised. Some panels, like ones from Panasonic, manage to make this nearly invisible. But it's not really a big deal at all.

I am beginning to suspect your new control board is bad or that there is some consistent connection problem near it.

[madlee357]

Re: LG PLASMA 50PQ30 rainbow effect + dark screen

check 4 cold solder on the y sustain and the z sustain underneath the boards