no backlight on screen, tried different cables and new screens, bad MB

Hey guys,

I've done what i consider some serious troubleshooting on this Dell E5470.

I've tried 4 different LCD screens, 3 of which were orderd brand new.

I've tried 3 different video cables.

All of the above have resulted in screen displaying basically 0% backlight.

Yes i've used FN+F12 and i can see the bar is maxed out.

BIOS is latest and says backlight is full.

I've connected an external display it and looks perfectly fine.

It seems like the problem MUST be at the motherboard? Is that possible for the motherboard to not let the screen have backlight?

Also for FYI - the E5470 has 1 cable between the motherboard and screen. The part connects to the motherboard, one part to the screen, and one part to the webcam. I've tried unplugging the webcam too just in case, no luck.

There are NOT 2 or 3 different connections on the LCD itself, just one.

Also other strange things;

I've tried 2 brand new 1080p screens that are made for this model, both get zero backlight but can see the screen ok.

I've tried 1 brand new 1366x768 screen that is made for this model but it gets no backlight but additionally only the left side of the screen shows any picture, the right side has nothing (split down middle).

Thanks in advance

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Hi,

Most laptops have a lid switch which controls the backlighting. It is usually a magnetic switch with the switch in the lid and the magnet in the case or vise versa. Sometimes the switch is on or near to the Power button board and the magnet is in the lid.

Some have it where the backlight power supply goes thru the switch and feeds the backlight circuit in the screen whereas others use it to send a signal to the motherboard to switch the backlight on/off.

In your case it sounds like the latter (as there is no separate backlight power cable connected to the screen) where the switch causes a software control of the backlight power as opposed to a mechanical switch action cutting off the power.

The switch (magnet?) is usually located behind the lower section of the lid under the screen to either the left or right of the screen.

Unfortunately I cannot find a service manual for your model laptop so I cannot tell you exactly were it is located but hopefully this info may be of some help.

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Alex Parshall estará eternamente agradecido.
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