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Display brightness problem without power cord

I am facing a display brightness mismatch problem when I wake up my laptop from sleep or off-stage, like below. It seems like a flashlight from to bottom-right corner, and the left side is much darker.

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If I increase the brightness without the power cord attached, the difference in brightness becomes more visible.

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Now, if I attached my power cord and decreased the brightness, at some point, the left-bottom light showed up and for a moment, the left-bottom side is lighter than the bottom-right light. Then decreasing more, it almost balances the brightness of the whole screen like below. Decreasing the brightness to zero makes a fully dark screen.

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After the left-bottom light showed up (or after the fully dark stage), If I increase the brightness with the cord attached, the issue is fixed and stayed good even if I remove the power cord. The problem will reappear if I close the display to sleep mode or turns it off.

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I don't know what is the problem. Whether or not to change the display because after decreasing followed by increasing brightness, the display looks totally fine.

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That is very... interesting. It is a novel issue for me so I'm not sure if I can help.

Have you checked your power and sleep settings? In there, there are options for battery saver to treat the display differently on battery power versus direct connection.

It could possibly a hardware problem, but it could also be a software problem and for some reason it is not registering the sleep mode is over for *all* of the screen and is only sending a wake up signal to half of it. Really strange if so, but if you can confirm that you turn off all battery saver settings and every aspect of the power management and screen settings has no difference between battery mode and plugged in mode, if this issue still happens it is more likely a hardware issue than a software one.

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@erelectronics My power saver is off, and my power plan is system Balanced (system recommended). Also, this happens whether I have almost full or low battery power. Even with the attached power cord, I turn the laptop from sleep or off-stage.

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@dipayanbiswas what you have here, is a backlight strip that is failing (left hand side darker than right due to failing LED's). When you decrease the brightness you decrease the power, that allows the failing section to turn back on. The only fix would be repairing/replacing the backlight or continue to run the display at limited brightness.

I believe that for your models display, the LED backlight is part of the assembly. You would most likely have to replace the screen. Enjoy using it until it one day will stay black. Then you know what you will need to do.

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Thank you so much. I have been using the laptop with the issue for over two years. Are you sure that changing the display will resolve the issue?

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@dipayanbiswas when you replace the display assembly, you can check around the display connector. There should be a few capacitors that are commonly part of the backlight circuitry and those are the only other possibilities. In this case the chance of those capacitors being part of the error is really really slim, since the error can be corrected. When you look at your screen (1st picture) you can see that only the first 1/3 of the backlights are on, the rest are all dark. Now that is full power, when you then decrease the power they finally turn on. Yes, I am pretty convinced of this. If it would be my laptop, that is exactly what I would do.

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Thank you again for your thorough explanation and suggestion.

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9 times out of 10, this is a bad LCD. I ran into it once on a Lat E6440 with the early IGP LVDS board (>_<) and when I looked for the parts I needed I went to PartsPeople to see if they have the panel; they did, but the price seemed high for a unit that shipped with the AUO TN 768p LCD; bleh.

Ultimately I looked into upgrading things a bit, so I had to see which board I had; Dell had three models for those: Launch IGP (LVDS), AMD launch (iDP), and 2014/15 boards (all iDP? You need to verify but my experience tends to point to iDP for those boards, which makes panel swaps easier). Due to the PITA factor of the LVDS board (768p=30 pin, 900p=40-pin), I opted for a nice used assembly with less wear than the original unit and it came with the webcam which the unit did not at first so I suspect it was a gov't spec version based on the screen and lack of webcam in 2013. It turned the laptop into a totally different beast and I do not regret that decision. What I usually recommend people do with the screen is since it will be expensive anyway, buy the screen you want but make sure the cable works; otherwise, you have to swap both. If you bought a laptop with a base panel like 768p and it can be upgraded to FHD or 2K and the overall cost to dump the original is about the same in terms of cost it's worth it for most laptops. It's a BIT more complex due to the cable situation with some laptops but the reality is a lot of newer laptops since 2015 or so use iDP LCDs so the cable problem is gone if you can absolutely verify this; but if it's LVDS, you need both like I did. For upgrades, these days I usually shoot for 2K or 4K depending on the price since most laptops come with FHD panels, but these can be difficult if you have poor vision; I love a good 4K IPS LCD, but if you can't see well do not do this upgrade.

NOTE: some laptops with iDP STILL COME with "stripped down" cables for these garbage panels; if you see multiple part numbers you got one of these and need both. Dell did away with the dual P/N crap with the iDP E6440 :-). Throw the 768p LCD out and put an FHD panel in. I also know the E7440 is like this if you have the iDP board; most of those are, Dell got smart and only put that junky board+LCD pair on early units. If it says "iDP" on both of those AND THE DP/N ON YOUR BOARD WAS "iDP" you just needed the panel and go all in on a good LG FHD IPS LCD, but I think I threw an HP pulled Samsung LTN in that iDP E7440. Knowing how Dell can flag things in silence, it probably threw a firmware flag or had something that didn't work but does it matter when the warranty is long gone?

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Dipayan Biswas will be eternally grateful.
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