LG 37LH40 screen freezing when cold

[jaxmoto]

Hi guys. First let me say thank you for a great forum, without the knowledge here I would not have been able to fix my Vizio 42 that had bad inverter boards. Just as an FYI I replaced the LC420WU5 boards with LC420WX5 boards and they worked perfect and stay cool.... but it was the info here that led me to the fix.

On to the new problem....

I have had a LG 37" 37LH40-UA LCD tv for 3 years. 14 months ago I turned it on to a frozen screen with junk vertical lines displayed.

I tried turning it off/on, unplugging it and basic stuff and it finally started working. For about a month it was fine. Then it started doing it every time I turned it on and I started to notice what was happening.

When it it turned on and has not been on for 5+ hours (cold) the picture freezes with the junk vertical lines(mostly black, backlight is working). About 5 minutes after it is turned on it will start displaying about 5 frames per minute, all jumbled with junk but identifiable as the tv source. Within about 10 minutes the fps comes up to normal but there is still some garbage on the screen... and about 10-15 minutes in it starts to work normally and is 100% fine. The backlight is fine through all of this.

If it is turned on when warm (has only been off an hour or two) it works perfectly fine, picture comes up immediately.

I have tried turning features like 120hz and others off/on, but none of the options make any difference.

Just wondering if anyone knows the core cause of this problem? I figure it is the image processor board but want to get more input before doing anything. The problem is it has done this for 14 months, and although annoying it still works so I hate to take any action that could ruin it.

I was considering baking the board (I have done this with other circuit boards) but I don't know for sure if it is a simple solder re-seating issue or something more complex.

Any help would be greatly appreciated. Going to swap it for my newly fixed Vizio 42" for TV but would like to go back to using the LG as a monitor like I used to, which is impossible in it's current state.

[uberplasma]

Re: LG 37LH40 screen freezing when cold

hey
sounds like a thermal issue. I would check voltages first, then and hit the ic's with a laser thermometer and see what heats up(like to normal operating temperature) and what doesn't and that would pretty much let me know what to reflow. I might even try light pressure on suspect ic's to see if I could get the frame rate back before it reaches the 10-15 minute mark.

[Paul678]

Re: LG 37LH40 screen freezing when cold

Hi guys. First let me say thank you for a great forum, without the knowledge here I would not have been able to fix my Vizio 42 that had bad inverter boards. Just as an FYI I replaced the LC420WU5 boards with LC420WX5 boards and they worked perfect and stay cool.... but it was the info here that led me to the fix.

On to the new problem....

I have had a LG 37" 37LH40-UA LCD tv for 3 years. 14 months ago I turned it on to a frozen screen with junk vertical lines displayed.

I tried turning it off/on, unplugging it and basic stuff and it finally started working. For about a month it was fine. Then it started doing it every time I turned it on and I started to notice what was happening.

When it it turned on and has not been on for 5+ hours (cold) the picture freezes with the junk vertical lines(mostly black, backlight is working). About 5 minutes after it is turned on it will start displaying about 5 frames per minute, all jumbled with junk but identifiable as the tv source. Within about 10 minutes the fps comes up to normal but there is still some garbage on the screen... and about 10-15 minutes in it starts to work normally and is 100% fine. The backlight is fine through all of this.

If it is turned on when warm (has only been off an hour or two) it works perfectly fine, picture comes up immediately.

I have tried turning features like 120hz and others off/on, but none of the options make any difference.

Just wondering if anyone knows the core cause of this problem? I figure it is the image processor board but want to get more input before doing anything. The problem is it has done this for 14 months, and although annoying it still works so I hate to take any action that could ruin it.

I was considering baking the board (I have done this with other circuit boards) but I don't know for sure if it is a simple solder re-seating issue or something more complex.

Any help would be greatly appreciated. Going to swap it for my newly fixed Vizio 42" for TV but would like to go back to using the LG as a monitor like I used to, which is impossible in it's current state.

I would try letting it cool off really good, and then turn it on,
while using a hair dryer on the circuit boards, to see if you can
accelerate normal functioning. It doesn't sound like it's
on the power supply.

That might allow you to find the trouble area.....

[tom66]

Re: LG 37LH40 screen freezing when cold

These LGs made around this time have loads of bad capacitor issues, so open your TV up and have a look... and take some pictures for the rest of us. I had an LG with a "similar" symptom; it would take around 15 minutes to power up (but nothing appeared on the display at all.) If it was still warm, it would power up very quickly. Four bad caps were replaced. It has worked perfectly for 8 months now.

[jaxmoto]

Re: LG 37LH40 screen freezing when cold

These LGs made around this time have loads of bad capacitor issues, so open your TV up and have a look... and take some pictures for the rest of us. I had an LG with a "similar" symptom; it would take around 15 minutes to power up (but nothing appeared on the display at all.) If it was still warm, it would power up very quickly. Four bad caps were replaced. It has worked perfectly for 8 months now.

I actually opened it up after posting just to make sure it wasn't a popped cap. This TV uses only 2 boards, a combined power/inverter board and a image processing board. The power board only has a few standard caps and they all look fine (I repair small computer LCD's all the time so I know what to look for). The image board uses all solid caps.

Every part of both boards was cool to the touch when I had the back off and when I turned it back on it is fine (had been using it prior).

That is the tough thing about this TV, once I am past that initial 15 minutes it is 4-5 hours before it does it again. It needs a full 12 hours or so to go back to the full 15 minutes of screwing up before it is fine.

I did learn a lot about the LG issues here and elsewhere... I will never buy LG again, or buy brands that use LG innards (so far Vizio and Dell I know about, I'm sure there are more.)

At this point I think I'm down to a bad solder seat on the imaging board... that is the only way to explain it. Attached are some pictures in case it does help anyone diagnose.

[tom66]

Re: LG 37LH40 screen freezing when cold

Those caps could be bad, even without bulging. Do you have a digital multimeter?

It could be a BGA issue... try pressing on the processors while it is in the screwing-up mode.

[jaxmoto]

Re: LG 37LH40 screen freezing when cold

Those caps could be bad, even without bulging. Do you have a digital multimeter?

It could be a BGA issue... try pressing on the processors while it is in the screwing-up mode.

I do have a good digital meter... is there any way to test caps still on the board?

Going to try to put pressure on the chips to see if that helps, probably have to wait till late tonight or tomorrow.

[tom66]

Re: LG 37LH40 screen freezing when cold

I do have a good digital meter... is there any way to test caps still on the board?

Going to try to put pressure on the chips to see if that helps, probably have to wait till late tonight or tomorrow.

Although you can't test caps with a conventional multimeter, you can test the effect of bad caps, which is low voltages on the power supply outputs. Can you post a close-up shot of the power supply connector?

[jaxmoto]

Re: LG 37LH40 screen freezing when cold

Although you can't test caps with a conventional multimeter, you can test the effect of bad caps, which is low voltages on the power supply outputs. Can you post a close-up shot of the power supply connector?

I'm assuming this is the one you were looking for?

[tom66]

Re: LG 37LH40 screen freezing when cold

You have some Samyoung capacitors. This is unfortunate, because they do not fail often (Samyoung are a subsidiary of United Chemi-Con, one of the largest capacitor manufacturers in the world.) Anyway, I see a 5.2V rail and a 26V rail. Check the voltages on the corresponding pins, relative to the frame of the TV.

[jaxmoto]

Re: LG 37LH40 screen freezing when cold

Hard to test everything at once so all I got to at this point was physically testing the chips on the main board to see if any sort of pressure caused any difference.... nothing at all.

In looking at how fast the boards heat up I'm now under more of an impression that it may be in the panel itself. The boards are up to operating temps within 3-4 minutes, yet the issue continues. The only thing that heats up slowly is the panel as all the combined parts generate heat.

Will get on the voltage testing in the morning when it has reset again. Hopefully it is something there because neither the main board or the panel are cost effective to fix, but the power board seems to be fairly common for $30-$40.

[tom66]

Re: LG 37LH40 screen freezing when cold

Hard to test everything at once so all I got to at this point was physically testing the chips on the main board to see if any sort of pressure caused any difference.... nothing at all.

In looking at how fast the boards heat up I'm now under more of an impression that it may be in the panel itself. The boards are up to operating temps within 3-4 minutes, yet the issue continues. The only thing that heats up slowly is the panel as all the combined parts generate heat.

Will get on the voltage testing in the morning when it has reset again. Hopefully it is something there because neither the main board or the panel are cost effective to fix, but the power board seems to be fairly common for $30-$40.

Well, it's unlikely to be the panel, because it's "digital" noise, if that makes sense. If you had lines or a blurry picture it could be a panel problem. The main board is getting confused. It *could* be the T-con.

[jaxmoto]

Re: LG 37LH40 screen freezing when cold

You have some Samyoung capacitors. This is unfortunate, because they do not fail often (Samyoung are a subsidiary of United Chemi-Con, one of the largest capacitor manufacturers in the world.) Anyway, I see a 5.2V rail and a 26V rail. Check the voltages on the corresponding pins, relative to the frame of the TV.

Sorry for the delay, been sick...

Tried out the voltages. There is the 5.2v which is running very close at 5.19v (tv on or off) and the 20v which is actually running at 21.7v (tv on only). It is impossible to tell if it says 26/20 next tot he plug, but the output ranges on the other side show 20v.

That is a pretty big overvolt but I'm not sure why that would cause the current issue of taking ~15 minutes to operate properly (voltage stays the same when cold/warm).

All the caps are Samyoung, however I have had to replace a number of this brand on LCD monitors.

First, any advice on if the 21.7v would cause issues? Also, if I were to want a full cap replacement set where should I go to use the badcaps supplier? (in the US).

Thanks.

[tom66]

Re: LG 37LH40 screen freezing when cold

Sorry for the delay, been sick...

Tried out the voltages. There is the 5.2v which is running very close at 5.19v (tv on or off) and the 20v which is actually running at 21.7v (tv on only). It is impossible to tell if it says 26/20 next tot he plug, but the output ranges on the other side show 20v.

That is a pretty overvolt but I'm not sure why that would cause the current issue of taking ~15 minutes to operate properly (voltage stays the same when cold/warm).

All the caps are Samyoung, however I have had to replace a number of this brand on LCD monitors.

First, any advice on if the 21.7v would cause issues? Also, if I were to want a full cap replacement set where should I go to use the badcaps supplier? (in the US).

Thanks.

I think the 20V is just for audio. It is a little high, though. After operating the unit for several minutes, do any of the caps get hot? I'm thinking it's more likely to be a T-con or main board issue, though.

[jaxmoto]

Re: LG 37LH40 screen freezing when cold

I think the 20V is just for audio. It is a little high, though. After operating the unit for several minutes, do any of the caps get hot? I'm thinking it's more likely to be a T-con or main board issue, though.

None of the caps on the power board are getting hot. The only things that actually do get hot are the chips on the main board, which 2 have heatsinks so I assume they were meant to get that hot.

When you say the T-con.... there is a small board at the top of the screen that connects via the two ribbon cables to the main board, is that the one?

Also, with the ribbons disconnected from the small board on top of the LCD should I be just getting a blank image or would there be digital junk signal all over the screen? When I disconnect them I get even more junk all over...

[tom66]

Re: LG 37LH40 screen freezing when cold

When you say the T-con.... there is a small board at the top of the screen that connects via the two ribbon cables to the main board, is that the one?

Yes

Also, with the ribbons disconnected from the small board on top of the LCD should I be just getting a blank image or would there be digital junk signal all over the screen? When I disconnect them I get even more junk all over...

I would expect a black image as the cable also carries power.

[jaxmoto]

Re: LG 37LH40 screen freezing when cold

Well it appears that those boards, the T-Con, are what is causing the issue. It isn't purely digital distortion in the "bad" state, some of it looks like bleeding and blurriness.

I would try baking them but unfortunately the ribbon that runs to the lcd panel is permanently mounted on each of those boards at the top of the lcd.

At this point it is back together and I'm just going to leave it as-is and hope it keeps going like it has.

On the plus side, thanks to the help of previous posts in badcaps, I got a 42" Vizio going for a total of $80. With the newer WX5 inverter boards it actually runs much cooler than the LG 37.

[tom66]

Re: LG 37LH40 screen freezing when cold

Well it appears that those boards, the T-Con, are what is causing the issue. It isn't purely digital distortion in the "bad" state, some of it looks like bleeding and blurriness.

I would try baking them but unfortunately the ribbon that runs to the lcd panel is permanently mounted on each of those boards at the top of the lcd.

You're kidding?! The ribbons are bonded to the T-con? Are these manufacturers trying to make these TVs disposable toys?! How much does a connector cost! The T-con is one of the most common failures on LCD TVs. Can you take a picture?

The fault you describe sounds like T-con or panel issues.

[budm]

Re: LG 37LH40 screen freezing when cold

By the way, what is the model of your 42' VIZIO? VO42LFHDTV10A?