faithie999
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E6420 display backlight flickers/goes out

when i boot my E6420 with AC adapter connected, the backlight doesn't come on. (i can see the screen image with a flashlight so the LCD is working).

with the computer booted, when i remove the AC, the backlight comes on at full brilliance but it flickers and flashes.  (flicker--very quick dimming;  flickering--very quick alternating between LCD on and totally off).

then when i reconnect AC, the screen dims to the level it would be on battery (dimmer than on AC) but still flickers--but the flashing is gone.

if i boot with AC not connected, the backlight works properly for about 10 seconds, then the backlights flashes between on and off every 1/2 second.  after a couple of minutes, the frequency of the flashing on/off goes to a couple of seconds, and when it is on it flickers.    so---flicker flicker flicker  flash off   flicker  flicker   flicker   flash off   etc.

i ran the pre-boot diagnostics.  it flags the LCD cable as bad, but the display is passed as OK.  I can easily replace the LCD cable, but any other ideas?

i thought maybe the DC in jack/cable was bad, but i replaced that to no avail.

thanks in advance

ken

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6 Replies
faithie999
1 Nickel

RE: E6420 display backlight flickers/goes out

in the second sentence, i meant to say:

flickering--very quick alternating between backlight fully on and then dim but not off;  flashing--quickly alternating between backlight fully on and fully off

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9 Rhodium

RE: E6420 display backlight flickers/goes out

Attach an external monitor -- if it displays OK, no flickering -- chances are it's the display panel that needs to be replaced.  If it flickers as well, it's the GPU -- meaning a replacement mainboard is needed.

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Moderator
Moderator

RE: E6420 display backlight flickers/goes out

Hi FAITHIE999.

Reseat the LCD cable and check. 

If you know the right part# of the system configuration - you can find the LCD cable here - http://bit.ly/2d31ie1

If not, then as advised by ejn63, either the LCD assembly or the motherboard needs to be replaced. 

Also, please click my DELL-username and write me a private conversation with the service tag and your contact details(Name and Email) for case records.

Let us know if you have any other queries.

Thanks and Regards,
DELL-Rishi
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faithie999
1 Nickel

RE: E6420 display backlight flickers/goes out

graphics work properly on an external monitor.

i will re-seat the LCD cable but i did that yesterday when i replaced the DC-in jack thinking that might have been the problem, since plugging and unplugging the power supply affects the screen's flashing/flickering behavior.

can you confirm that the inverter is built into the display panel?  i would not want to buy a new panel only to find out that the inverter is built into the motherboard.  

thanks

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9 Rhodium

RE: E6420 display backlight flickers/goes out

These systems do not use CCFL backlit screens -- there is no inverter (the backlight is LED and built into the display panel).

No one can guarantee you that it's the screen that's faulty - but it's the next part to replace.  If it does not solve the problem, it's a video chip issue and the mainboard would need replacement.

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faithie999
1 Nickel

RE: E6420 display backlight flickers/goes out

thanks for confirming that there is no inverter.

both the vga and HDMI output are flawless, mirroring the display while the display is doing its flashing/flickering/dimming thing.  i conclude that it's not the gpu.

i think i will try an LCD cable before replacing the display.   $4 vs $50 so worth the gamble IMHO.

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