Latitude E6420 LCD Backlight Syncing Issue cause a blown LCD

Hi, I recently purchased a brand new E6420 with a 1600x900 display screen. In the bios or anything out of windows, I can only dim the screen down to a minimum(LCD back light is obviously not off and visibly on) via the fn hot keys. Also this, applies to the preinstalled windows 7. I would rate the lowest setting to be a 4 out of 10, 10 being the brightest.

So now the problem, when I reinstalled a fresh windows 7(and another try with all the drivers installed in the correct order), i can dimm the LCD alot more than what was supported in the bios. I thought it was a new feature, but after dimming it to a complete off, I couldn't turn it back up. I fiddle with it by plugging in the power plug, and it came back on. I did this a few times, and the LCD backlight stop coming back on, its completely dead. I went into bios, turned the light up to max, reboot and it still stayed off. Plugged the LCD into another E6420, and it backlight was dead there also. So i concluded the LCD backlight is dead.

Since this laptop was less than a week old, dell replaced it with a new laptop. On this new laptop, i'm experiencing the same issue, is there anyways to prevent windows from over dimming this LCD screen? I believe it will blow up this new screen again if i accidently over dimm it again.

Also, i noticed the dimming icon that pops up on the preinstalled win7 is more responsive, and it actually shows the dimming level correctly. The updated version I installed, Dell Feature Enhancement Pack_APP_WIN_R312092, has a logo change, and the light level indicator does not move along with brightness of the screen correctly. My only solution now is to clean up the preinstalled windows 7, or nuke this laptop back to dell!

Please, can someone give me a good fix suggestion?? Or can anybody else confirm the LCD brightness toggle issue with windows 7 pro 64bit?

 

You have to install the drivers in just the right order to prevent the backlight from turning off. That order is in a thread somewhere, I haven't done it yet.

Interesting that your LCD was seemingly perma-broken, as I (and others) have been able to recover from turning off the backlight by opening Windows Mobility Center (Windows key + X) and dragging the brightness slider back up using a external light source to see the screen (a cell phone flash works great!)

As you've already experienced, once the backlight is off, using the function shortcut keys on the keyboard won't bring it back up again.

 

Seeing as this was your first post and you are claiming to have done something no other E6420 user has done - how about some proof? Not that I doubt you, but you are saying a software glitch can kill an E6420 display and that no one else has already done it. Screenshots? Text of chat logs with Dell? Anything? You say you swapped the panel to another E6420 so you must have a high level background. Help us understand how this happened.

 

I'm having a similar issue, which I'll try to describe a slightly different way. In my case, it is not simply the backlight. The sequence for me is:

1) Laptop is plugged in via supplied AC (no docking)
2) I have Windows 7 set to do nothing when I close the display (i.e. do not sleep)
3) When I close the display, it turns off as it should, both backlight and display itself. So far, normal, just like any other laptop.
4) When I re-open the display, most often (but not always), the display does not turn back on. It's not just the backlight - there's nothing on screen.
5) I can get the display back on by doing one of 2 things:
5a) Unplug the AC, which instantly turns on the display. After plugging back in, it stays on fine.
5b) Re-close the display, wait a moment, then re-open it. Again, it instantly powers back on.

It is NOT the case that the laptop is recovering from sleep - it's still running all the time at full CPU speed - just the display won't come back on.

 

Some questions that'll help steer me into the right direction:

1. Is this a machine given to you from the IT dept at work, or is it your personal machine?

2. If its your personal machine, did you perform a clean install of the operating system?

 

I followed this direction for installing the drivers. http://forum.notebookreview.com/del...n/587149-e6520-e6420-driver-install-list.html

Installing all those latest drivers in that order still allows me to dim to the turn off point. I attached a picture of the new software, and old version software. Hopes that sheds some light.

For Bokeh,

I still have the other laptop on hand was gonna return this week. What do you want me to do with it? I can take a pic of the bios brightness setting with a flash light shining into the screen, but i don't think that will prove much to you.

As for testing the LCD, i do have a high tech background, and I was searching the web forums, and it seems like this is the forum to sign up and ask at . Basically, i unplugged the old LCD, plugged it into the new new laptop, and it was still dead. I reversed new lcd back into old laptop, and it was good. I did this risking my new laptop cause i was i didn't believe software killed the back light myself, but this test was pretty conclusive to me to confirm the LCD death.

 

Also, I should mention I downloaded and used all the latest drivers from the Dell webpage for the E6420, except the following(which i got from the Intel or Nvidia website directly):
-Intel Chipset
-Intel Raid/AHCI drivers
-Intel Video Card
-Intel 6300 Wifi Nic
-Intel onboard gigabit nic
-Nvidia nvs 4200m

 

Sure- thanks for the help.
1) I am the IT department (translate: I've done this about a million times)
2) yes, clean install, just like I build all our machines. Roughly the same order as that thread that's floating around - but a stable order for sure.

We have 2 other E6420's, but haven't tried reproducing this issue on them yet. To some degree, it's not a disaster, since I use an E/Port 99% of the time. But, it does seem odd.

And the way I can get it back on via the AC plug and/or the display close/open is very odd.

(Perhaps I've inappropriately hijacked this thread - sorry.)

 

Ok - did some more tests today, and now the behavior really suggests a hardware issue, I think.

1) I did my clean install to a new hard drive. I still have the original Dell installed drive. Put that in, and same behavior, including what's below.

2) With the AC plugged in, when I reboot Win7, the screen turns off as it cycles power, as usual. But it doesn't turn back on. BIOS POST does not show, but the system starts, and then the screen turns back on by itself at the logon screen. At this point the backlight is dim and flickers its brightness. Unplugging the AC immediately snaps the brightness to the normal, bright and stable level. Plugging back in, the screen dims and flickers again. AFTER logging back in, I can reconnect the AC without the dimming coming back.

3) If I do the same while on battery, none of this happens and all is well.

4) IF I do the same while docked, also no issues and all is well.

So, it seems to be some issue with the AC, I guess? How the heck am I going to explain this behavior to Dell Support... That;ll take a while, I fear.

 

I had a bit of flickering when the screen dimmed down too much on my dead e6420. I think if you do that enough, it will kill the back light.