LG L1942T Vertical Lines that Mostly Fade Away

[printone2]

I am working on a an LG L1942T that is only one year old and has a problem of many vertical lines when it turns on, with or without any vga signal attached. As the panel warms up (30-60 seconds) the vertical lines for the most part all start working normally except one line on the right side of the screen. I would not expect it be bad caps, since the panel is so new, but the caps are primarily Sam Young brand. I do not know any history on this equipment, since it was donated. It does have a crack on one corner of the front plastic, so it may have seen some kind of abuse. None of the metal case or internal parts show any signs of wear of damage. The angle of the image card below gives the appearance that the caps are domed, but that is not the case.

I did not want to just start recapping on such a new panel, before I asked if this was a lost cause. One more thing the on-board menu appears to have horizontal lines missing from the picture making it hard to read the text. Like if you have an LED display but the top and bottom row of pixels are not turned on. Otherwise the picture looks good. The solder joints look fine to me. I would welcome some thoughts on what is the most likely issues.

[retiredcaps]

Re: LG L1942T Vertical Lines that Mostly Fade Away

only one year old

Wow, that is one dodgy design looking logic board.

Q602 or Q601 and that big blue colored resistor looks like a total afterthought?

[printone2]

Re: LG L1942T Vertical Lines that Mostly Fade Away

Wow, that is one dodgy design looking logic board.

Q602 or Q601 and that big blue colored resistor looks like a total afterthought?

Does that mean that the logic board is poorly designed and the problem that it has are not related to the fact that part of the front case has a crack? That means the problems are just as likely to be from design and component failure?

It looks like the vertical lines finally disappear and look normal, but the missing horizontal lines never really turn on.

Is this possibly a bad capacitor issue or is their some issue beyond the main board circuit that is the root problem?
Thanks.

[retiredcaps]

Re: LG L1942T Vertical Lines that Mostly Fade Away

If the problems clears up after 30 to 60 seconds, try this.

1) Let monitor sit until "cold" for some time.
2) Take hair dryer and heat up caps on logic board (or power, but one only board) for about 30 seconds.
3) See if lcd turns on and displays properly within the first 5 seconds.
4) Repeat test.

[printone2]

Re: LG L1942T Vertical Lines that Mostly Fade Away

If the problems clears up after 30 to 60 seconds, try this.

1) Let monitor sit until "cold" for some time.
2) Take hair dryer and heat up caps on logic board (or power, but one only board) for about 30 seconds.
3) See if lcd turns on and displays properly within the first 5 seconds.
4) Repeat test.

It did not make any difference when I heated the logic board. But what I did notice is that after the vertical lines all look normal, if I shut off the power to the panel and turn it back on, the sames vertical lines again go through the process of gradually getting the correct colors just as if the panel had been started from a cold boot.

This indicated to me that it is not a bad solder joint warming up or a component getting up to temp, my guess is that it is more like a capacitor finally building up to the right voltage or amperage to work properly. Is that anywhere close to right?

[printone2]

Re: LG L1942T Vertical Lines that Mostly Fade Away

It did not make any difference when I heated the logic board. But what I did notice is that after the vertical lines all look normal, if I shut off the power to the panel and turn it back on, the sames vertical lines again go through the process of gradually getting the correct colors just as if the panel had been started from a cold boot.

This indicated to me that it is not a bad solder joint warming up or a component getting up to temp, my guess is that it is more like a capacitor finally building up to the right voltage or amperage to work properly. Is that anywhere close to right?

I replaced the three 470uf 35v sam young caps on the IPS and the one 470uf 16v on the image board. I did not have any 1000uf 16v caps or I would have replaced a few of them.

I also measured the power going to the image board. Power seemed normal on the 5v (5.2v) pins, but the following pins looked odd to me. I thought that the voltage might be different after the panel was on and the colors had adjusted, but it was not. What was odd were the following pins:
These values are with the lamps switched on.

On 3.3
DIM 2.6
MS 3.7

When the lamps are off and the panel is still plugged in the readings are 0.0, 0.0 and .1v respectively. I do not know if any of these last readings are odd, but I thought the readings with the lamps on might all be closer to 3.3v. Anyone want to venture a guess if the two last pins are indicating a problem?

Changing these caps did not change any of the panel performance. It still has vertical lines, which adjust to a normal setting once on for a few minutes.

[PlainBill]

Re: LG L1942T Vertical Lines that Mostly Fade Away

I replaced the three 470uf 35v sam young caps on the IPS and the one 470uf 16v on the image board. I did not have any 1000uf 16v caps or I would have replaced a few of them.

I also measured the power going to the image board. Power seemed normal on the 5v (5.2v) pins, but the following pins looked odd to me. I thought that the voltage might be different after the panel was on and the colors had adjusted, but it was not. What was odd were the following pins:
These values are with the lamps switched on.

On 3.3
DIM 2.6
MS 3.7

When the lamps are off and the panel is still plugged in the readings are 0.0, 0.0 and .1v respectively. I do not know if any of these last readings are odd, but I thought the readings with the lamps on might all be closer to 3.3v. Anyone want to venture a guess if the two last pins are indicating a problem?

Changing these caps did not change any of the panel performance. It still has vertical lines, which adjust to a normal setting once on for a few minutes.

On is the inverter control 3.3V for On, 0V for Off. Dim is the analog brightness line. That frequently goes to 0V when the backlights are turned off. I have no idea what MS represents. I wasn't able to trace it visually because of the white areas.

PlainBill

[printone2]

Re: LG L1942T Vertical Lines that Mostly Fade Away

On is the inverter control 3.3V for On, 0V for Off. Dim is the analog brightness line. That frequently goes to 0V when the backlights are turned off. I have no idea what MS represents. I wasn't able to trace it visually because of the white areas.

PlainBill

Then does this still appear to possibly be a cap problem? I could order caps to replace the rest of the board if this symptom seems consistent with a capacitor that is not coming up to normal operating function until it is on for a while and once it is shut off it must start the process over again.

[printone2]

Re: LG L1942T Vertical Lines that Mostly Fade Away

Then does this still appear to possibly be a cap problem? I could order caps to replace the rest of the board if this symptom seems consistent with a capacitor that is not coming up to normal operating function until it is on for a while and once it is shut off it must start the process over again.

I replaced the caps on the image board and all but two very little ones on the IPS. But nothing has changed. The vertical lines slowly turn on to their proper color from the top down, so the image is readable. I have also reseated the ribbon cables from the image card to the tab connector that controls the rows and columns. Nothing seems to make a difference.

Any clues on what is causing this?

[Badcappy]

Re: LG L1942T Vertical Lines that Mostly Fade Away

Does (lightly!) tapping the panel surface at the edges where the lines are with a soft blunt object do anything?

[printone2]

Re: LG L1942T Vertical Lines that Mostly Fade Away

Does (lightly!) tapping the panel surface at the edges where the lines are with a soft blunt object do anything?

No, it does not make a difference, but the metal case is very stiff and I do not think that the pencil erase is stiff enough to make a difference. It does make a ripple on the surface as you would expect.

I noticed that it takes 30 seconds to come to normal colors regardless of if the panel is warm. It always begins to fix itself from the top down in a gradual wave down the screen. It is like the tide coming in from the top nice and gradual.

The other observation is that when I turn it on and off the pattern of where the vertical lines are is not the same. Sometimes the middle of the screen looks normal and sometimes is has vertical lines. Most of the time the vertical lines are the width of an icon. If I move the icon during the warm up period, the lines do not follow the icon, but when I turn it off and on again the vertical column tends to follow the new location of the icon.

[alexanna]

Re: LG L1942T Vertical Lines that Mostly Fade Away

Have you let the monitor run for any length of time?
I should ask how long have you let it run?

[printone2]

Re: LG L1942T Vertical Lines that Mostly Fade Away

Have you let the monitor run for any length of time?
I should ask how long have you let it run?

It has been on for six hours today and still reacts the same. Since it sends a different pattern of lines after each shut off, it makes me think it is an image card problem. I am using a VGA input now, I do not have a digital input setup. Any guesses about whether a digital input would make any difference?

[alexanna]

Re: LG L1942T Vertical Lines that Mostly Fade Away

It has been on for six hours today and still reacts the same. Since it sends a different pattern of lines after each shut off, it makes me think it is an image card problem. I am using a VGA input now, I do not have a digital input setup. Any guesses about whether a digital input would make any difference?

No I don't, I just have had some strange stuff happen after a recap. I just wanted to make sure you let it get good and warm.
Al

[printone2]

Re: LG L1942T Vertical Lines that Mostly Fade Away

No I don't, I just have had some strange stuff happen after a recap. I just wanted to make sure you let it get good and warm.
Al

Well after leaving it on all night the pattern of vertical lines have now stabilized when I turn it on and off. Now the vertical lines appear in the same columns and with the same colors every time that I cycle the power on the panel.

[alexanna]

Re: LG L1942T Vertical Lines that Mostly Fade Away

Well after leaving it on all night the pattern of vertical lines have now stabilized when I turn it on and off. Now the vertical lines appear in the same columns and with the same colors every time that I cycle the power on the panel.

Is there any way you could try flexing the logic board in various spots with a small wooden dowel or something similar,
I am thinking of a poor solder joint or PCB issue.

[printone2]

Re: LG L1942T Vertical Lines that Mostly Fade Away

Is there any way you could try flexing the logic board in various spots with a small wooden dowel or something similar,
I am thinking of a poor solder joint or PCB issue.

I think that will be hard to do. Now that I can see the line pattern is consistent it makes me doubt that the problem is with the IC chip that creates the image. Could I have some weak smd caps on the image card or the tabs that control the vertical and horizontal lines. I have never tried to test these kinds of devices, except a smd fuse.

[printone2]

Re: LG L1942T Vertical Lines that Mostly Fade Away

I think that will be hard to do. Now that I can see the line pattern is consistent it makes me doubt that the problem is with the IC chip that creates the image. Could I have some weak smd caps on the image card or the tabs that control the vertical and horizontal lines. I have never tried to test these kinds of devices, except a smd fuse.

Have not tested the smd caps, but did configure a digital video input. The digital feed did not make any difference.