No video on laptop screen, but OK on external monitor

I have a Toshiba Satellite X205-S7483 laptop with Windows 10 Home installed. Recently, the screen went black while I was using it. I powered it down and started back up. All seemed OK (fan running, HD light flashing, etc.) except nothing on the screen. Here are the symptoms and what I have tried so far, watching the laptop screen while starting up with an external monitor.........

1. The screen is totally black during POST. Tried looking for the Toshiba logo image with a flashlight...nothing.
2. Once Windows starts, there is faint light on the screen...bluish white, but very faint. When Windows is shut down, the light goes away and the screen is totally black again, all the way to power down.
3. If I unplug the power cable to the LCD Inverter board (While Windows is up) the light goes away.
4. I have tried a used screen and a used LCD inverter board purchased on Ebay...same results. I'm assuming they are OK. Is there a way to prove the LCD Inverter board is working OK?
5. The cable from the motherboard to the screen looks OK, and the connections are good

I'm at a loss and curious if the issue could be with the graphics part on the motherboard, rather than the screen. Would a failing graphics card/chip allow my external monitor work OK but not the laptop screen? Is there a sure way to prove which area is causing the failure? Any help is appreciated.

 

I do not own this model laptop but to answer you last question. I have never seen a graphics chip go out like that. Most of the graphics chips are made into the CPU's now. On an expensive laptop, there are some with a separate grapics chip but that is the exception. Graphics chip usually work or they don't, or they display artifacts within the picture. You have done everything right in working on it. It sounds like your laptop display is not getting the correct voltage from the laptop. It requres 2 different voltages (ahhh maybe 3) from the laptop. I personally dont work on LCD because I am pacemaker dependant and I don't want to risk a shock. You can get a bad shock from some of these things so be careful. Here is a video that may help you. By the way, I had a laptop with a problem like this a little while back and never got it fixed so good luck. Here is a video that might help you.. Good luck

 

gray1, thank you for the response...very much appreciated. In my research, I did view this video, along with some others by the same person. He is good and offers some good suggestions...especially with the voltage checking. I did not pursue the solution in this video because the laptop he was working on had video on the screen, but no backlight. My issue is the opposite...I have backlight, but no video. I am "assuming" that suggests the inverter and the screen LED bulbs are OK, especially since I get the same results from two different screens and two different inverters. However, since I get normal video on an external monitor through the VGA connector, that suggests the video circuitry is working....hence my dilemma. I hate giving up since I suspect this is a simple fix somewhere...but, sometimes the catch is not worth the chase. (-: Thanks again.....Ron.

 

He is a good guy and a good teacher. I know he had a different problem than you do. But he checked the voltage coming out of the computer connecter to the screen. One side was 19V and the other side was 3.3 volts I believe. Since your laptop screen is not working at all, I suspect that you do not have one of these voltages coming out of your laptop to the inverter. Therefore your screen is not working at all. I am not a profesional or a computer tech but that would be my best guess. Just be careful and not get shocked. Cheers