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Released 2017, Model Number 81B5.

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Display not working after replacement.

I got this laptop from a relative with a broken screen. It had some dead rows and would only work if it was at certain angles if you wiggled it around first. It seemed like a short in the cable because the webcam also wouldn't work. I replaced the whole lid assembly with one on eBay. the webcam works now but the display still won't come on. Windows only detects the external monitor as the only screen. Does anyone have any ideas on what I can do to troubleshoot? Thanks for the help!

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Is the replacement the exact same model number? Recheck cable.

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I don't see a model number on the cable and I don't want to take the display out of the lid. Is there a different way to check?

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Hi @jamesolsen57324,

Just verifying that you disconnected the battery from the motherboard, before removing/replacing the screen?

With the laptop turned on, try shining a flashlight at an angle close to the laptop screen and check if you can detect any images at all on the screen.

They will be very faint if they are there so trying in a darkened room may help to see them.

If you can see images then there's a backlight problem or if there are no images to be seen, it may be an LCD power supply problem or LVDS cable problem.

Please verify the model number of the laptop or the motherboard (printed on motherboard e.g. BM5706? or LA-E55???? perhaps) as the schematics may be needed to find out what's wrong and where the problem is

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Thanks @jayeff I do think it is a backlight problem. I tried the flashlight and saw the Lenovo logo at boot. I did wear an esd wristband and unplugged the battery. The model number is p2028dap. Thanks!

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@jamesolsen57324

The number you posted doesn't produce any results at all when searching online.

I can't find the schematics for a 720-12IKB but looking online for a 720-13IKB=LA-E551P and 720-15IKB=LA-E552P so you would think it would something near these numbers but I can't find anything except that the schematics for your board is unavailable at this time.

Since you tried "wiggling" the video cable I'm wondering if you accidentally blew a fuse on the motherboard that feeds the back light power (faulty video cable perhaps in original screen?)

Maybe check for any components on the motherboard with an "F" designation, close to the video cable connector or at least within a couple of inches anyway.

If you find any fuses, measure them with an Ohmmeter and the battery disconnected from the motherboard. They should test short circuit i.e. 0.00 Ohms if they're OK and open circuit (OL)if they're not.

Mostly they are 36V 3A smd package (you may have to measure it e.g. 0603 is one size). Don't worry about the voltage (36V) being too high. It is the current rating that is important. That's just the way the fuses are configured.

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I looked to see if there were any fuses but I couldn't find any. Is there something I can check before I look at the other side of the board?

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@jamesolsen57324

Post a close up image or two of the video cable connector area of the board just in case you missed it.

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Thanks! There should be an image now.

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