42 lg3000 TV, white screen with black border

[SchrodingersCat]

Hi!
I am after getting a faulty TV that im hoping to repair for myself.
The screen itself looks perfect.
It turns on but the problem seems to be something internal as it takes a few minutes for screen to come on to a load of colours and black border around the edges. However, these disappear after about 5-10 mins.

The model no: 42lg3000-za.aekdljg

I will attach an image of to explain myself better. I was wondering if anyone would have any idea of what could be wrong with it?

[t.j.]

Re: 42 lg3000 TV, white screen with black border

open it up an look for obvious faults ie: visible blown caps, or burn marks on board! got dmm, dl service manual an check voltages of psu! try this reseat all the cabling inside!

[SchrodingersCat]

Re: 42 lg3000 TV, white screen with black border

Thanks for the reply t.j. Before I open it up, does it look like any common fault that you have seen before?

[Th3_uN1Qu3]

Re: 42 lg3000 TV, white screen with black border

This kind of artifacts can be caused by either a bad tcon or a bad main board. Since you say it takes a while to come on, bad caps or cracked solder joints are likely.

[SchrodingersCat]

Re: 42 lg3000 TV, white screen with black border

Thanks for the reply Th3_uN1Qu3. The proper picture doesnt actually appear at all (apologies for the bad wording in the original post), after the weird white/coloured picture appear with the black borders, the black borders then disappear leaving nothing. I will sit down some quiet evening so and open it up to see if there are any loose connections with the TCON board, check the caps and the voltages, and see of there are any cracked solder joints. I might even chance buying a replacement TCON board and mainboard on ebay if I cant find anything visibly wrong and see if that fixes it. It would probably work out cheaper than buying a new one, as they are about 50e ($60) each on ebay. http://www.ebay.co.uk/itm/MAIN-BD-EA...9ecd151&_uhb=1
http://www.ebay.co.uk/itm/CONTROL-BD...9fe59d3&_uhb=1

[tom66]

Re: 42 lg3000 TV, white screen with black border

Just make sure that the LCD panel in this TV is the same as the T-con is made for. LG used cheaper panels in the more recent xxLG3000 TVs.

[SchrodingersCat]

Re: 42 lg3000 TV, white screen with black border

Cheers tom66, il do that.

[Jahson]

Re: 42 lg3000 TV, white screen with black border

yea thats is very true tom66 about different tcon for this model.

[SchrodingersCat]

Re: 42 lg3000 TV, white screen with black border

I will attach a sequence of images showing progression of the display on the TV from when it is powered up. The display briefly flashes, then goes to black. Then a white image appears surrounded by black borders. Then the borders disappear and finally a bright white image is left indefinitely. There is also some colorful pixilation if the display is viewed close up (see close up image attached).

I also noticed that the issue is also intermittent. After I left the tv on for 30min yesterday, I unplugged it and plugged it in again. Then it seemed to be working again (see last image below). If it unplugged and plugged it in again there was around a 50:50 chance that it would power up in working order, or show the weird black borders again.

[SchrodingersCat]

Re: 42 lg3000 TV, white screen with black border

So, I opened it up to have a look with my fluke multimeter.

There were no visible scorching on any of the boards, or any bulging caps. I removed and reinserted each cable harness, seeing if there was any change when I powered up the TV at each stage (there wasnt). Looking at the PSU, and from its silkscreen markings on the board, the voltage outputs vs. my measured outputs are as follows:

5.2v: 5.12v measured
12v: 12.34v measured
16.5v: 16.54v measured
24v: 24.32v measured
PWM-DIM: 1.137v measured
on/off: 5.01v measured
ACD: 5.01v measured
DRI: 3.212v measured
Error: 0v measured

So all the voltages seemed to be fine, which I assume means that the PSU is fine. So I brought my attention to the TCON board. I measured 12v on both ends of the fuse. After a bit of fiddling, I finally got it off the chassis for inspection (see front and back image below). However, the long ferrite around one of the two flat ribbon cables to the LCD display must have been cracked, as it broke in half when I took the board off (see image). Does anyone know how sensitive these cables to a cracked ferrite? Could this be causing my problem?

I also wiggled and applied pressure around the mainboard and the TCON board while the TV was powered up to see if it made a difference, but it did not. I assume that this lowers the possibility that there is a bad solder connection somewhere.

Assuming that the issue is arising due to a bad mainboard or TCON board, is there any way that I can know for sure which one it is before I invest in a replacement board off ebay? If there isnt, which one would be more likely to go so that I could buy and try that part first? Or would anyone have any suggestion what I could try testing next?

I have access to a digital oscilliscope, decent soldering iron, signal generator, etc, too if thats any use. I would love to get this TV working again and save it from the recycling depot!

[Th3_uN1Qu3]

Re: 42 lg3000 TV, white screen with black border

About that ferrite - you can just superglue it back in place and it'll do its job. I don't think it has anything to do with the picture problem.

[vinceroger69]

Re: 42 lg3000 TV, white screen with black border

it may be worth heating each board up first with a hair dryer to see if it makes any difference with how quick the tv starts up as in last picture in post 9 i would start with the power board heat it up then try switching on then try each other board if you find heating one board makes it start faster maybe heat a little area a time untill you narrow the area that effects starting up ok.

[SchrodingersCat]

Re: 42 lg3000 TV, white screen with black border

Thanks for the replies Th3_uN1Qu3 and vinceroger69. I will have a go with the superglue and the hot air gun in the day or so and tell you how I get on.

[kevinm34232]

Re: 42 lg3000 TV, white screen with black border

SchrodingersCat I had a 26" LG with similar issue, turned out to be a main board issue as I replaced T-Con with same result. I tried heating and cooling of boards first and it seemed like it might have been the t-con but in the end after elimination it was a problem in the main board, guessing the VPU. Mine would turn on then freeze parts of screen, or whole screen, eventually after some time it would start working normally...