LG display sporadic screen issues

[thedosmann]

LG Display model - lc550eud(se)(m1)
This is a custom 55" modified as a 55" touchscreen computer
The computer board is on its own power supply and connected to the LG display via HDMI cable
All components are internal

The unit was purchased from an overseas supplier and put into service mid-January.
After about 2 weeks in service the screen started displaying problems similar to what I've seen in searches on here and other places when a bad t-con is suspected. A combination of screen flicker, distortion, image roll, and it usually would degrade to a frozen screen but sometimes correct itself. There was no rhyme or reason, no consistency. Sometimes it would go 4-5 days without messing up. Usually a power on/off cycle would fix. Sometimes it would have to be off for a while and sometimes it would correct itself.
Troubleshooting started on the PC side and it was verified not to be the PC board or software.
I went over the boards on the TV side and did not notice any bad caps or other obvious issues. I found a t-con board and ordered it. I replaced the t-con board but with no joy. I took it back out and put the old board back in. I then re-accessed the boards on the TV side and noticed a tiny bad place on the mainboard. I would upload an image but this is my first post.
I ordered a new board and put it in and I'm now letting the unit stay up for a few days to verify the fix. I will update in a few days.

[thedosmann]

Re: LG display sporadic screen issues

Here is a pic of what I found on the mainboard

[tom66]

Re: LG display sporadic screen issues

That looks to have been reworked. Possibly factory original.

[thedosmann]

Re: LG display sporadic screen issues

I deemed as bad. What you think?

[tom66]

Re: LG display sporadic screen issues

It just looks to be coated in flux to me, and the flux has dried up leaving a brownish/blackish residue. While it could be bad, I can't see a component failing violently (and permanently) causing an intermittent issue. I would be considering the LCD panel itself -- possibly a tab bond fault.

[thedosmann]

Re: LG display sporadic screen issues

The replacement board looked no where near that nasty at that spot and the cap right beside that bit of ugly shows heat at the bottom but I'm leaving it up for a few days so if it goes south again I'll look next to a tab-bond issue. Thanks. I'll have to study up on what a tab-bond is.

[tom66]

Re: LG display sporadic screen issues

Tab bond issue (symptoms vary widely) and fix:
http://www.youtube.com/watch?v=purk_SyiT44

[thedosmann]

Re: LG display sporadic screen issues

Well, it went south this morning. So I'm off to Tab-Bond land. The touch glass will complicate this a tad but let's see what I can tear up.

[thedosmann]

Re: LG display sporadic screen issues

The Tab - bond fix doesn't seem to apply. I followed the directions and touching the ribbons has no effect. I went ahead and added the shims but no effect. The problem has changed now to going to a black screen shortly after power on. Sometimes it will show a good screen for a second and sometimes a white screen with the power down countdown barely showing. After a few seconds it just goes to a black screen.

[thedosmann]

Re: LG display sporadic screen issues

Below are some pics of the boards. When I power on it shows a white screen that goes to black in a few seconds. Either the component that was going out went or its another issue. It only stays lit for a few seconds but I can see the power down countdown just faintly before it goes black sometimes.

[thedosmann]

Re: LG display sporadic screen issues

With the PC board as input it doesn't power down and the screen remains white.

[thedosmann]

Re: LG display sporadic screen issues

It seems somewhere in the mix the t-con did go out. I replaced it and the screen is displaying ok but intermittently messing up. It will either blink off for a second or distort for a second and go back. It is happening every minute or so or sometimes it will wait for a few minutes. I checked the shims and still little or no distortion if I push in on the ribbons.

Edit
The longer it stays up the less frequently it messes up.

[thedosmann]

Re: LG display sporadic screen issues

I've replaced the main board, t-con board, and applied the tab bond fix as described here - http://www.youtube.com/watch?v=purk_SyiT44.
Currently when I power on it will blink to black screen, distort, or otherwise mess up for a second or two and go back to a normal screen. This happens about every 5-10 seconds. This becomes less frequent the longer it stays on until it seems to stop messing up completely. I'm not sure if it completely quits doing this as I cannot watch it every minute. I'm leaving it up for now to see if it goes south but obviously there is still an issue. Any suggestions?

[ben7]

Re: LG display sporadic screen issues

I've replaced the main board, t-con board, and applied the tab bond fix as described here - http://www.youtube.com/watch?v=purk_SyiT44.
Currently when I power on it will blink to black screen, distort, or otherwise mess up for a second or two and go back to a normal screen. This happens about every 5-10 seconds. This becomes less frequent the longer it stays on until it seems to stop messing up completely. I'm not sure if it completely quits doing this as I cannot watch it every minute. I'm leaving it up for now to see if it goes south but obviously there is still an issue. Any suggestions?

Those symptoms sound like bad capacitors! The capacitor ESR decreases when the capacitor warms up. If there are no visible bad capacitors, then you should get an ESR meter to test them. (ESR = Equivalent Series Resistance)

[thedosmann]

Re: LG display sporadic screen issues

Thanks for the reply. I will take another look at the boards. Do you suggest an area to concentrate on? Power, inverter, ..I have replaced the t-con and main board so I feel they should be OK?

[tom66]

Re: LG display sporadic screen issues

You can attempt to heat parts of the TV and see if you can clear the fault quicker; if you do find a part which makes the picture get better, that part is suspect.

[thedosmann]

Re: LG display sporadic screen issues

Is it possible the tab-bound fix may have may have created too much of a bond causing it to take time to properly connect? Once the set is on for a few hours I can disconnect the input and while it goes into power down countdown I can reconnect the input and no issues show. If I let it power down and wait a minute or two and power back on it starts with the bad behavior again for a few minutes. Also, the sides of the panel metal frame get very hot to the touch not the top and bottom just the sides. I can hold my fingers on it but it's very hot.

[tom66]

Re: LG display sporadic screen issues

That is unlikely; but you can confirm it is not the screen by heating the parts -other- than the panel.

[thedosmann]

Re: LG display sporadic screen issues

It doesn't matter now because it lost picture again. Back light still glowing but no picture..just black screen. I will look at the boards to see if something blew.

[thedosmann]

Re: LG display sporadic screen issues

No obvious problems anywhere. Checked v on F1 of t-con and it shows 11.87 on both ends with back light on. Is there a fuse beyond that or where to from here?