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.
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.
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.
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). For the test purpose, you can buy a new backlight lamp here. 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.
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.
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.
I removed the screen bezel and connected my test backlight lamp.
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.
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February 28th, 2008 at 6:53 am
OK… I think I have a good little problem for someone to try to solve. My laptop backlight wont light up. Everything works and looks great when I send the video to an external monitor (my TV). I can also see the picture on the laptop monitor if I look closely and use a flashlight. I replace the inverter board… didnt fix it. I took the lcd apart and I have a new backlight as well as the old backlight resting comfortably outside the lcd panel so that I can see it clearly. Here is what I see. Please Help. When I turn the laptop on, the backlight flashes once real quick, and thats all I get. I don’t know if the inverter I put in there is just another bad inverter board or if this is some sort of power supply issue or something else. Please Help
February 26th, 2008 at 10:31 pm
Am I correct in assuming it isn’t the inverter, backlight or cable if I get no power to the screen, and nothing on an external monitor?
My display failed on my A70 after disassembling due to the overheating issue. Laptop powers on, hd fires up, no beeps, just no display. Reseated inverter wires, ground and video on the board…still nothing. Took it all apart (again), reseated the CPU and heatsink….still nothing.
Any ideas for troubleshooting? I’m really stumped! Thanks
February 24th, 2008 at 12:12 pm
At last!
I fixed my LCD!
I found some backlight bulbs from the LCDs of old laptops that were sent for recycle!!!
I made the appropriate connections, I re-assembled my LCD and everything worked fine!!!!!!!!!!!
February 21st, 2008 at 4:50 pm
[...] problem still could be related to the screen backlight. Unfortunately, the only way to find out is testing the laptop with another working backlight attached. Try reducing the screen brightness a little bit, it might [...]
February 1st, 2008 at 12:28 am
Thanx cj2600…
I used an AC multimeter to measure the output of the inverter while the input was normally connected to the laptop.
The output was more than 1000V AC!
This means that the inverter works (since it is supposed to have a high voltage AC output) and this is what I call bad news.
Since the inverter works my only solution is to buy a new LCD screen?
Right?
Could something else be wrong?
Toshiba service replaces the LCD with 940 euros!!!!! Of course this is not an option, I better buy a new laptop. On ebay the price is much better, around 200 euros but then I am worrying if the screen will be ok after doing the long trip from USA or China to Greece.
If there is no other case for something to test if it is not working then probably I will have to risk it…
Please suggest me if I should check another part before ordering the new LCD.
Thanx in advance!
Andreas
January 31st, 2008 at 8:34 pm
Andreas,
I don’t know. Toshiba doesn’t provide this information and I’ve never tried measuring it myself.
January 30th, 2008 at 3:49 am
cj2600 do you know what is the input-output voltage characteristics of any of the inverters:
G71C00011121 (toshiba part number: P000354880)
or
G71C00011221 (toshiba part number: P000439470)
Thanx in advance!
January 22nd, 2008 at 11:05 pm
Mike D,
Did you buy and swapped the whole display assembly or you bought all parts one by one? Did you try replacing parts one by one? First inverter, then LCD and finally the video cable.
January 22nd, 2008 at 9:16 pm
Hi,
I have a Dell Inspiron 9200 and the LCD display is extremely faint:
I can see a very faint image so think I don’t have a working backlight in the LCD display.
I can plug in an external VGA screen and it works well
I purchased from ebay a new display/inverter/cable and it still is has a very faint image.
I noticed the LCD plugged into the ATI video card (while the VGA plugged into the motherboard) so got a videocard on ebay; same issue.
So I have replaced everything but the motherboard. Are there special voltages the inverter needs to enable the backlight?
I don’t see the on off switch for this computer and a google search didn’t help yet either. Do you know where the on/off switch is? I would think the computer would go into hibernate mode if this was an issue.
Any other ideas of where to go next? I am pretty hardware/computer proficient but very frustrated with this issue.
Thanks,
Mike
January 19th, 2008 at 1:46 pm
Bahula Smith,
I think it will but I’m not sure 100%. I don’t work a lot with IBM laptops.
Here’s what you can try for testing the backlight lamp inside the new LCD screen.
Disconnect the LCD screen on your laptop from the inverter board and plug the new screen instead. In this setup the video signal still goes to the old screen and you still should see a faint image on the old screen, but the inverter board will provide power for the backlight lamp inside the new screen. If the lamp inside the new screen is good, it should light up (I assume the inverter board is working fine).
Check out if you can light up the backlight lamp inside the new screen.