Lenovo L2440pwC "2secs to black"

[Teredactle]

Hi all,

I just picked up a Lenovo L2440pwC monitor from work, it was left outside the IT office door (this is what they do when they get rid of stuff they don't need/doesn't work, etc).

It is exhibiting the "2secs to black" behaviour exactly; I turn it on, it shows the logo for 2 secs, then it goes black; if I shine a light on the LCD, I can see that the info is being displayed.

I used this post as a reference, but there is another issue with the LCD in that, not the 2sec to black: https://www.badcaps.net/forum/showthread.php?t=27034

I took a lot of pictures, looked at the caps, and they don't "look" bad, but of course, that is not always the case. The back of the boards look fine too; no burn marks that I can notice anywhere. I have attached the pictures I took.

-Would you suggest that I just buy caps (about 15 of them) and replace all of them FIRST?
-Or should I try and test with a CFL first, to see if the inverter circuits are working? I'm a bit confused if I need to take the bulb apart to connect the wires, or if I can connect directly to the outside of the bulb. I think if I understand correctly, I need to cut it open to connect to the "filament" connections as the voltage coming out of the connectors on the board is already converted.

From the guide, I conclude that this would be the order of things that could be bad:
1. Caps
2. Bad Transformer
3. Bad CCFL
4. Bad Solder joints


Thanks in advance!

[Teredactle]

Re: Lenovo L2440pwC "2secs to black"

Ok, so after reading the CFL post I decided to make one, I had a 13W bulb in one of my closets that I took apart in order to use for testing.

This monitor has two outputs for the light tubes, they look identical. When using the bulb to test and switching power on:

1.With the wires inserted in WHITE and RED (picture reference), the bulb lights up all the way (then off in 2sec).

2.When I have the wires inserted in BLUE and GREY (picture reference), the bulb lights up 1/3 of the way and it making an "arcing" noise.

Is #2 normal?

Thanks!

[Lumberjack777]

Re: Lenovo L2440pwC "2secs to black"

No, it's not normal. That's why when you plugged the test bulb into the White and Red, you still had 2 seconds to black. The bad bulbs were still in play. Sounds to me like you have either a bad connection, or bad bulb(s) on the Blue and Grey wires. You tested this problem perfectly. You'll need to tear it apart and check out those bulbs and connections on the Blue and Grey wires.

[Lumberjack777]

Re: Lenovo L2440pwC "2secs to black"

On 2nd thought. Here's what normally happens when you use test bulbs. When you plug the connector from the good bulbs to the test lamp it will still go out after 2 seconds because the bad bulbs are being used on the other wires. When you connect the test bulbs to the connector with the bad bulbs, it should light up and stay lit, because the bad bulbs are out of the circuit. You mean the test bulb lit up 1/3rd and made arcing noises? In that case it might be the inverter.

[Teredactle]

Re: Lenovo L2440pwC "2secs to black"

Thanks for the feedback. I will explain in a bit more detail what I did.

The picture in my second post is the output to the monitor bulbs. There are two of these connectors on the board (can be seen here, left side https://www.badcaps.net/forum/attach...7&d=1442080380)

I unplugged the monitor bulbs from these connectors. I'm not sure what the colors of these plugs mean, blue+gray, and white+red.

I used a 13W CFL with a tail, and plugged it in each pair:
Connector 1:
B+G
W+R
Connector 2:
B+G
W+R

So 4 tests, each time, I would power cycle.

Same thing exhibited, 2sec to black, the only difference being when the bulb was plugged into W+R, it would "fully light up", while plugged into B+G it would be lit up 1/3 of the way (of W+R) and make this popping/arcing noise.

No, I'm thinking a few things (would appreciate feedback)

1) All outputs seem to behave the same, on for 2 secs, then off (I will retest B+G, but i believe this was the case as well, off after 2 secs)
2) If B+G barely lights up the bulb, on each of the connectors, could it mean that this voltage out is normal lower then W+R? the CFL bulbs make this noise if they don't get enough juice, is that not the case (i.e. they are not the dimmable kind)... not sure on this
3) I would like to test out the bulbs on the monitor actually, (as it is when the monitor is on for 2 secs, it's pretty dim) and have quite a few transformers (the wall pluging kind) with diff DC outputs - what should these be generally tested with? V/A? If they are good I don't want to burn them out.
4) I think I saw someone post that they just connected them to transformer outputs, seems risky, may need to read up more on this.

I bought replacement caps already, so looks like I'm committed here...

Cheers

[budm]

Re: Lenovo L2440pwC "2secs to black"

When I verify the function of the inverter board, I use at least TWO test lamps.
You monitor has 4 lamps total, 1 pair for the top edge of the screen and another pair for the bottom edge of the screen.
When you test the inverter board, you will put two lamps on one set of the lamp connector socket, leave the other lamp connector socket of the inveret board still connected to the set of lamps in the monitor. So now you have two test lamps to lamp socket, and the two lamps of the monitor on another set of socket, if the backlights stay on then you know that you have one set of lamp is bad, if it does not then you do the same thing by switching the test lamps to the other socket and connected the other lamps that you disconnected in the beginning back in place where the test lamps were connected to.
When you only have one test lamp connected, the inverter will still go into protection mode because it will sense open connection of the other 3 lamps.

[Teredactle]

Re: Lenovo L2440pwC "2secs to black"

Thanks for the feedback on this. I haven't had much time lately to try this and I didn't have a second lamp, I'm hoping that next week I can try to troubleshoot as you indicated above and see what results I get, then go from there! Will then post the results.

Thanks again

[Teredactle]

Re: Lenovo L2440pwC "2secs to black"

When I verify the function of the inverter board, I use at least TWO test lamps.
You monitor has 4 lamps total, 1 pair for the top edge of the screen and another pair for the bottom edge of the screen.
When you test the inverter board, you will put two lamps on one set of the lamp connector socket, leave the other lamp connector socket of the inveret board still connected to the set of lamps in the monitor. So now you have two test lamps to lamp socket, and the two lamps of the monitor on another set of socket, if the backlights stay on then you know that you have one set of lamp is bad, if it does not then you do the same thing by switching the test lamps to the other socket and connected the other lamps that you disconnected in the beginning back in place where the test lamps were connected to.
When you only have one test lamp connected, the inverter will still go into protection mode because it will sense open connection of the other 3 lamps.

I finally had time to actually do this today, even though I got the second build about a week or so ago. Sucks when you don't have "tool shop"... condo living; I have to store this 24" LCD in a dresser drawer..

Anyway. I tested as recommended, and regardless of testing the top or the bottom, the same thing. The two laps would light up for a bit, then go off. I even captured video of this.

Before replacing the caps, I will test out the other components the guide suggest at, which could also cause the 2sec2black and perhaps avoid unneeded hours spent de/soldering.

I guess the good news is that the CCFLs may not be bad; the teardown to replace those things seem pretty involved and delicate; I wish there was a way to test them easily.

Cheers

[Joe Black]

Re: Lenovo L2440pwC "2secs to black"

-Would you suggest that I just buy caps (about 15 of them) and replace all of them FIRST?

Always a good idea. As one member has it in his sig, quality of electronics is directly proportional to quality of electrolytics. So, if you're able to, yes, go ahead and replace caps. Although, you don't HAVE to. Kind of your call

From the guide, I conclude that this would be the order of things that could be bad:
1. Caps
2. Bad Transformer
3. Bad CCFL
4. Bad Solder joints

5. MOSFET inverter drivers. (D812 & D805 it seems?) You should check both of them as next step, along with both transformers (inverter, ofc).