Troubleshooting backlight failure

posted in: Screen, Troubleshooting | 209

This laptop came for repair because of the LCD screen backlight failure. My customer complained that the laptop LCD screen is black but the laptop works with an external monitor.
Here are my steps for troubleshooting this laptop with the backlight failure.

First of all, I tested this laptop with an external monitor connected to the VGA port and the external monitor worked absolutely fine. I was able to get crystal clear image on the external screen even though the internal screen didn’t light up. If the external screen works fine, then most likely there is nothing wrong with the video card.

Notebook display assembly diagram

After that I took a closer look at the laptop LCD and noticed that the screen is not completely black. The laptop screen still works but the image is very very dull, you barely can see it. It means that the screen still gets data signal from the video card, but for some reason the backlight lamp doesn’t work.
From my experience I know that this problem can be related the lid close switch, faulty inverter board or bad backlight lamp. I checked them one by one.

If you have a similar problem, make sure the lid close witch moves freely. The lid switch is a small button located close to the LCD screen. This button triggers the hibernation or sleep mode when the screen is closed. If the lid close switch is dirty, it might get stuck inside the laptop case and cut off the power from the inverter board. The inverter board works as a power supply for the backlight lamp and if there is no power coming to the inverter board, the backlight lamp will not light up either.

Image with pinkish tone

In my case the lid button worked properly, it didn’t stuck inside the case. When I was pressing on the button very fast, I was able to light up the screen but only for a fraction of a second. The image wasn’t bright and it had a pinkish tone. A pinkish tone usually indicates a problem with the backlight lamp, not the inverter board.

Replaced inverter board

Even though I suspected the backlight failure, I decided to test this laptop with a new inverter board just in case. But it didn’t help. The screen didn’t light up even after I replace the inverter board. So, I was right, this problem is not related to the inverter board.

Connected known good backlight lamp

Finally, I disconnected the screen backlight lamp connector from the inverter board and connected my test backlight lamp (I removed it from another cracked screen). You can find a new backlight lamp on eBay. Try to find a backlight with the connector already attached to it, so you can plug it into the inverter board. Make sure the connector on the backlight lamp is similar to the connector on your LCD screen.

My backlight lamp works fine

As soon as I turned on the laptop, my backlight lamp lighted up. Yep, that’s the problem. The laptop screen has a faulty backlight lamp.

Here’s another laptop with backlight failure

This laptop video fails in a little bit different way. In this case the backlight lamp hasn’t failed completely.

Background has reddish tone

The laptop starts with video on the screen but the background has reddish tone, the screen flickers and it makes noticeable buzzing noise coming from the backlight and inverter area. After a few minutes the backlight turns off by itself and the buzzing noise stops. When the backlight is off, the image on the screen is still visible but it’s very dark.

Backlight lamp connected

I removed the screen bezel and connected my test backlight lamp.

Backlight works

My test backlight works absolutely fine. The lamp doesn’t flicker and there is no buzzing noise. So, this laptop needs a new backlight lamp.


209 Responses

  1. Albert

    Thanks, after about a month of searching the wrong places, this article has unwittingly shown me a hack for my laptop’s issue till i can afford a technician and parts (the best i can fix with a screwdriver is probably a door knob). Turns out that my laptop while having the same symptoms described here but without the pink hue, behaves if i turn the brightness way down and watch it that way.the buzzing sound goes away and the screen stays on.. probably cos it puts less pressure on the weak backlight.

  2. My brand new Gateway NE5R41u the screen stays black I hooked it up to my desk top monitor and still nothing it stays black. power turns on there is sound just black screen. help

  3. Acer purchased at Future Shop, Best Buy Canadian subsidiary had a backlight failure. As it was still under warranty I took it in for repair. I am unsure of the backlight failure, but when returned they had performed a system recovery. I suspect this was done to deflect responsibility from Acer and onto the customer. When returned now one USB port not functioning. I did all updates, system and drivers, but no joy. Returned the laptop to them and was again threatened with a system recovery. Luckily I have a system image.

  4. Gustavo Rubio

    I have a toshiba p205-s6347 problem went I turn on the laptop the screen are black but in the buckground see the intel and toshiba logo, but I noted that went I touch with my fingers wet the inverter over the circuits on the left side the backlight comes on, inverter new, backlight new, bus video cable new, i know that is missing voltage on the inverter any option to fix this issue

  5. mohammed

    i have check scree n inverter board but i cant get the lcd scree n back litght

  6. Worked for me. Old Advent 7201. Clear on external monitor but very faint on laptop screen. Culprit was dirt in the lid close sensor. This is a small sprung tab in the bottom of the left hand of the two sockets into which the lid clips sit.

    Thanks

  7. @ B.T.JAIRAM,

    It’s possible the video cable got disconnected from the LCD screen.
    It’s necessary to disassemble the laptop and reconnect the video cable on the back of the screen. Also check video connector on the motherboard.

  8. I have a Dell XPS M1530 with a complete dark screen. I’ve replaced the LCD Panel, the inverter board and the video cable. Nothing. One thing to note here is there isn’t even a shadow on the screen either. System boots fine and displays fine on an external monitor. I’ve been through this severla times, rechecked all connections, etc. This is the way it came to me, so none of the new parts changed the problem. What else could possibly be casuing a completely black screen (no shadow)???

  9. B.T.JAIRAM

    my lenovo 3000 n100 fell and the lcd moniter is completly off when opened 45 degrees and beyond and when just pressed lt frame from top it light-up or otherwise when i pressed at back on point it works upto 90 degrees up
    will you let us know the circuit connections to open up the monitor and repair
    thanks

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