Display brightness problem without power cord

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?