LG 42 PQ3000 with mal-discharge and colour banding.

[Dang]

Hi, I have an LG 42PQ3000 with the above issues, I've found that adjusting the SET_dn pot anticlockwise has helped to eradicate some of the dots, problem is this colour banding is not helping, I believe the banding is an issue with the control board but I'm not sure. The way the colour banding shows it's self is with definite colour patches and bands where shadows or bright reflected light should be, for instance, my silver car has red patches that should be a bright silver. I've noticed that changing the picture mode has a big effect, going from "standard" to "cinema" can give the menus a yellow stain with some parts flashing depending on what sub option you choose, gamma being an obvious one. It all seems like an LVDS issue but not sure, if anyone can please confirm? thanks, Andy.

[tom66]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

Pictures of the fault would help?

[Dang]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

They would but I didn't have a camera at hand so tried explaining it, I'll get some up soon, thanks Tom66.

[Dang]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

Hi again, OK, so what I've discovered is HDMI ports 1 and 2 produce the colour banding described above, where as port 3 is fine suggesting a main board issue, another problem I have found is that the screen will suddenly go blank and you can here that something has turned off, those usual "power" sounds have gone, I've still got sound and the Tv is on showing a constant blue light, just no picture. I'm going to have a look for dry/cold joints but was wondering if anyone knows if this is a known fault and so is there a known cure available? I've searched on line but can't find much, thanks.

[Dang]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

I should add, I've now noticed that the colour banding is an intermittent fault, most of the time there, sometimes not.

[Dang]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

Hello again, so has anyone any idea why the picture will suddenly go off whilst still keeping sound? for sure something in the back cuts out, just not sure what's causing it, thanks.

[tom66]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

Does the panel glow go as well?
Vs/Va/etc present?
Blinking light on control board?
If there's an optical audio output, does that go off too?

[Dang]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

No, the screen just switches off, the usual "buzz" of electronics working goes so it's like all that's required to power that side of things just switches off. I've not as yet had a good look at it, I was hoping it may of been a known fault so if you have an idea that would great to hear, thanks again, Andy.

[tom66]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

No ideas here, sorry. Just general checks.

[Dang]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

Decided to go back to this one once more and try and suss out exactly what's going on. So after trying to test the Tv and still turning it's self off a few times here and there, it finally decides it doesn't want to play ball any more, power supply clicks on and then off, tried a few times and it's the same. Obviously something some where had blown short, what ever was causing the the Tv to turn off randomly had finally blown properly, as it goes it turns out to be the X-main.

It was quite interesting trying to work out what had gone wrong as I was seeing a lot of shorts everywhere in the circuit, places that were fine were isolated by diodes, places that weren't, after tracing back, all pointed to the power transistors and indeed four of the power transistors near the output stage had blown, I guess one was intermittent and finally blew taking the rest with it, they are 45F122's, of course it's not conclusive, only changing them will give that answer and this is where I ask my question, I can buy a set of five of these transistors from Ebay for £14, are there any good but cheaper replacements out there, they seem to be rated for 300v/200a pulsed and is there anything else I may need to look out for?

Once the power side of things is sorted(maldischarge etc) I will need to look at the colour banding issue, my guess is a bad logic/LVDS board.

Photos just coming.

Why so many problems with this tv?????????

[tom66]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

It's a cheap crappy LG plasma... their 720p sets have always been a little, iffy... especially their 42" sets...

If you change the IGBTs it's highly recommended to replace the driver IC for them as well (usually a small SMD package on the bottom of the board.)

[Dang]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

It's a cheap crappy LG plasma... their 720p sets have always been a little, iffy... especially their 42" sets...

If you change the IGBTs it's highly recommended to replace the driver IC for them as well (usually a small SMD package on the bottom of the board.)

Thanks, it's starting to sound like a new board is the better option, it's only £17.25.

[tom66]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

Yes at that price it's a no brainer to buy a new board.

[Dang]

Re: LG 42 PQ3000 with mal-discharge and colour banding.

Well, got it even cheaper at £15, fingers crossed it sorts out the power issue.