LG 47LM640T Lines, trying to start?

[Ecorecycler]

Hi,

As can be seen in the photos, there are lines all across the screen on this TV. The don't really change much. I've tried pressing the TAB bonds and nothing happens.

There is a stripe that moves up periodically- every few seconds like something is trying to start up maybe. I've tried to show it in the photos.

I've checked the DC voltages are present on the PSU board but haven't done much more yet. There doesn't appear to be a TCON on this unit, so I'm guessing it's either part of the mainboard or it's part of the panel.
Menu's don't make any difference but the remote does turn the TV on and off.

I'm thinking of starting by checking to see if I can find any shorts on the main board.... Any ideas?

Thanks

[tom66]

Re: LG 47LM640T Lines, trying to start?

Lines like that are rarely a good sign and can indicate a bad LCD panel. One test you can do is to remove one of the two ribbon cables going from the main board to the power board. Power the TV up with one removed and see if you get half a picture. Repeat for the other ribbon. If either brings back half the picture the panel is shorted, unfortunately this would make it scrap.

[Ecorecycler]

Re: LG 47LM640T Lines, trying to start?

I did try removing the cable to each half and the problem persisted on the side plugged in.
Would this mean it's more likely to be a TCON fault?
I found out the TCON and Mainboard are the same board on these.

Thanks

[Ecorecycler]

Re: LG 47LM640T Lines, trying to start?

I just tried it again. When the left hand is plugged in(looking at the TV). The screen is almost bank, but seems to get brighter and dims. It doesn't respond to the remote. With the right hand side plugged in there are a few lines but no where near as many. The brightness changes continually but again no menus or anything else.

[tom66]

Re: LG 47LM640T Lines, trying to start?

In general that would indicate the possibility of a panel failure. I suggest checking the panel tabs for water damage, corrosion or burn marks.

[Ecorecycler]

Re: LG 47LM640T Lines, trying to start?

That's very helpful. Thanks Tom. I did have a look at them earlier to see if it was a TAB bond issue. They seemed to be OK. I'll have another look. If they seem OK, do you think it's likely to be the TCON/Main board?

[Alastair E]

Re: LG 47LM640T Lines, trying to start?

That's very helpful. Thanks Tom. I did have a look at them earlier to see if it was a TAB bond issue. They seemed to be OK. I'll have another look. If they seem OK, do you think it's likely to be the TCON/Main board?

Personally--I think its the LCD Panel itself....

[Ecorecycler]

Re: LG 47LM640T Lines, trying to start?

Well looks like you're right again Tom. Someone must have spilt a drink down it :/
The traces don't look too bad. I might just clean it up, check the components and reflow the solder.
Sorry about the image quality.

Thanks for the help again.

[tom66]

Re: LG 47LM640T Lines, trying to start?

It's eaten into the flat flex - will be very tricky. About the only thing you can do is to scrap off the outer coating of that flat flex and expose the inner copper, then solder a wire to the appropriate pad. And then hope no other damage has been done to the actual driver ICs on the tabs.

[Ecorecycler]

Re: LG 47LM640T Lines, trying to start?

Well spotted. I think it looks like another return. The guy said he had it from new and it just stopped working. Said it hadn't been opened but some bits of tape were taken off, a screw missing and scratch marks on the screws.
You've saved me a lot of time. Thanks.

[tom66]

Re: LG 47LM640T Lines, trying to start?

Sigh, when will panel makers include some kind of basic water sealing - wouldn't even need to be advanced. I'm sure many panels die for no reason other than getting wet...

[Ecorecycler]

Re: LG 47LM640T Lines, trying to start?

Guess it's cheaper not to include it, keeps sales up and they don't have to cover the damage in the warranty. Win, win for them!

[freakaftr8]

Re: LG 47LM640T Lines, trying to start?

Yea you should see this crappy Proscan 39 inch I picked up to repair an led backlight issue. The tabs are not mated to any cooling heat sync. Exposed and the carrier PCBs are taped to the plastic frame of the TV!! On the bottom of course. They get hot. Panel made by AUO surprisedly but cheap. Left side of the screen is dimmer and dithered. The tcon is built into the panel PCBs also. No cooling. Its a recipe for disaster! Thermal runaway soon and also I can touch the PCBs from under the TV. Bunk design. Don't get me started on the led backlights! They are literally melting away from lack of cooling. The strips bend up and down against the back of rhw panel like a rollercoaster