DELL Latitude E6420 Does No Longer Show Display

Hi Boris_yo,

I would suggest you to connect an external monitor with the system and check if you are able to get proper display on external monitor.

Here are the steps:

• Shut down the system.
• Connect the external monitor with the Blue VGA connector (VGA cable/connector is the normal cable that connects the monitor to the desktop system).
• Restart the system and power on the external monitor, press the Fn key and hold it down and while holding it down, press the F8 key this would switch the display to the external monitor.
• Check if you are getting the display on the external monitor.

Please share if you have received any error codes or beep codes when you power on the computer.

Please run the LCD built in self-test. Here are the steps:

• To run the LCD BIST (Built in Self-test) Press and hold the D key on the keyboard while pressing the power button, then release both at the same time.
• This will initiate a grey screen, then Red, then Blue, then Green then White, to allow you to inspect the entire LCD for color purity on each screen and to better identify defect such as cracks in the LCD or stuck pixels that may not be apparent in a normal viewing mode.

Please share the findings.

Awaiting your response.

DELL-GARIMA thanks, the test worked and I could see colors you mentioned. I do not have necessary equipment to test on external monitor though.

Hi Boris_yo,

Since the test passed it means that the LCD is fine. I would suggest you to re seat the LCD cable.

You may refer to the link http://bit.ly/188KCSV to check the manual on how to re seat the LCD cable. Select the display option from the content table.

Note: Please follow the safety instructions mentioned on the manual.

Awaiting your response.

:emotion-1: Hello DELL-GARIMA. What I did was the following:

1. Reseating 2 of LCD connectors - LCD screen works (as we determined previously), still no display

2. Removing one of 2 memory modules and placing first into slot of another

3. Disabling in BIOS internet NIC, wireless NIC, eSATA, USB ports, Serial ports, Intel Hyper Threading, Intel Visualisation etc.

4. Resetting CMOS

Only resetting CMOS helped but it was shortlived because after saving changes in BIOS and restarting laptop again, I once again could not see anything displayed. Once again I resetted CMOS and monitor was displaying until at the BIOS post screen I was offfered to press F2 for starting testing environment. I hit F2 and was brought into testing environment but nothing was displayed. Again for the 3rd time I resetted CMOS and somehow managed to enter testing environment by holding Fn and Power keys. Testing environment did not detect problems with video card but it showed error with LCD screen, picture of which you can find with link to my Dropbox album folder where you can see additional information. I Googled this error and it was said that newer BIOS versions have problems with previously manufactured laptops thus it does not detect LCD wire so consider this false positive and not hardware according to what this thread says.

I ran video card test in testing environment and recorded what I saw which you can check by going to my Dropbox account and you will find link below. I don't know if this is what video test supposed to be but it seems weird since expected something that makes sense. Here I see distorted line going from top to bottom and disappears after which nothing else happens until I hit Esc. But here is where it gets interesting: previously I could set which video card to use in BIOS. It was feature called nVidia Optimus but now, I no longer see that option or any related option where I can set my video card. Strangely, first time booting to BIOS works after resetting CMOS and in system information I see "Intel HD Graphics", its version and memory size. Of course should I save changes and restart laptop, I can no longer see anything on screen again. Is this problem with my dedicated video card? (nVidia NVS 4200M) Which brings me to question: why Dell laptops with primary and dedicated video card cannot fallback to default primary video card or video card that works? If I have dedicated and primary video card, what use will primary card make if it is not usable in scenario dedicated video card fails?

Please take a look at the picture of 2 LCD screen connectors here. I want to know what does first connector and what does second. Maybe I could plug out connector that is connected to dedicated video card and leave one connected to primary video card? Even if Dell implemented "fallback to default working video card" feature, what if my case is complex as failing video card is detected as working thus BIOS switches back to it everytime?

Here is a link to my Dropbox account which has troubleshooting shots I took and also video clip of me testing video card in testing environment. If you cannot access resources outside your workplace then let me know, I will think of something.

Thanks for helping me.

I don't think the CMOS battery is to blame because it either powers BIOS chip to keep information or it doesn't. In my case it does and there is nothing wrong with it. Let me remind you again that I cannot continue further BIOS message after computer's POST. There's nothing on display so I can do nothing until I pull out CMOS battery again and my computer POSTS so this cycle continues. I can't even access internal BIOS hardware testing environment because displays shows nothing so we can forget about everything that comes past POST screen.

First fully boot up system, when it's fully loaded, then. press/hold these 3 keys "ctrl" "alt" and "delete" all at same time for 2 seconds.

Then let go all keys, then press the down arrow key two (2) times ... the key arrow pointing down is in the right lower corner. of the keyboard,  Then press enter.

At that point you will or should see the display turn on.

Give it a try.

So is the screen totally blacked out, or can you see some  light behind the dark screen? If you can still see light behind the dark screen, it's the display inverter board., 

Also connect a external screen to the VGA output of the laptop, if you can't find a vga cable,  If your taptop
has an HDMI port, connect it to a tv with a HDMI port.

boot up system/laptop, when it's fully loaded, then pres the CTRL ALT DELETE keys, hold them down at the same time for 2 seconds.and let go.

Then, find the ARROW key pointig down (it's in the right lower corner of the keyboard, then press DOWN ARROW key 2 times, then press enter.

At this point the display will show up.

Hello,

My E6420 just tonight started showing the same issue.  The backlight on the LCD works (I can see it) but the display is not displaying any text or graphics.

Did you ever get this resolved?  What did you do?

I can share that an external monitor works OK for me.  

Sounds like you have a Bad Display or a Bad Display Cable/Ribbon/Connection.  It's not the Video Card since you can view on a a External Monitor.  The Display Cable/Ribbon is the Cheaper of the two so I'd try and Replace that first(or at the very least check and make sure the cable/ribbon connection is seated properly on both sides display side/motherboard side).  If you have the ribbon check to see if there's crack on it. if there is...good possibility it's the problem

If you look into the screen and see no backlight but can see text/graphics then we know it's still getting data and that's when we know it's not a data cable and possibly the inverter board/light but if all you can see is the light and no image whatsoever.  It's either the display/data cable/ribbon or the display itself.

If you  can't view through a external display, then it's the video card which is typically integrated onto motherboard.

1. Seat cable/ribbon properly and check if a crack on the ribbon(no money needed for this step).

2. Replace Cable/Ribbon(inexpensive compared to replacing screen).

3. Replace Display

Yes I did and in my case it was malfunctioned onboard nVidia graphics chip because no external means worked for trying to output signal. I could have chip extracted from motherboard and replaced with new one which I could order from eBay, I could pay DELL authorized service center over $800 to have motherboard replaced due to expired warranty but only paid them $60 for basic checkup which led to quote of over $800 from them. I could easily buy same new model from eBay so what I did was ordered motherboard on eBay for $130 and personally replaced old with new motherboard thus saving $670 and enjoying the experience along the way.

Sounds like my problem might have been a little different.  Here's some details on my symptoms and how I got it working again.

Symptoms

• LCD backlight was on
• No text or graphics displayed 
• No BIOS screen
• External monitor worked OK
• Pressing D on powerup caused the internal LCD panel to flash black, white, red, green, blue, etc

Troubleshooting:

• I had a E6430 at my disposal as well - so I used it to see what was working or not on the E6420
• At first, I removed the bottom panels from each laptop and routed the E6430 display cable to the E6420 motherboard.  I powered on E6420 and the display (now on the E6430) worked OK. 
• Likewise, I took the E6420 display cable and attached to the E6430.  When I powered on the E6430 the display (now on the E6420) did not work.
• This all lead me to believe the problem was in the LCD assembly on the E6420 since the problem followed the panel.
• I was going to swap inverters, but the inverter assemblies are different between the two computers.  
• Next, I swapped the LCD panel itself.
• When I put the E6430 panel into the E6420 - it worked.
• When I put the E6420 panel into the E6430 - it worked.
• So both LCD panels themselves work...  I figured the problem is probably in the cable between the LCD and the motherboard.
• However - when I reassembled everything - the E6420 was now working.

Resolution

• While not 100% confident, I suspect there was a bad connection on the back of the LCD panel of the E6420.  When I removed the cable (for troubleshooting) and re-attached it, the laptop and display began operating normally.

Hope this helps someone else down the road!

For reference, here's the E6420 service manual which aides in disassembly:  

ftp.dell.com/.../latitude-e6420_owner%27s%20manual_en-us.pdf

Thanks radef, I have the same problem I disconnected lcd but did not understand what cable you are referring to.

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