Video problems with Compaq CQ50

Repairing a CQ50.  Screen was out (very dim - no backlight). External VGA monitor looks fine, so it is not a video chip problem. Ordered new inverter, put it in, no change. Ordered new (used, from ebay) video cable, put it in, screen comes on for 2-10 seconds then goes out (dim picture still there, as before).

It does not always go out when it changes graphics modes; it sometimes goes out while still on the Compaq logo, so it is not a software problem. I figured it was a bad video cable connection. I flexed the screen and cable, pushed, pulled, wiggled all connectors on it while running, no change. Then I unplugged the video cable from the motherboard while running, plugged it back in, and the picture comes back for the same 2-10 seconds and goes out again!  I can repeat this as many times as I want, so I guess it is not the cable.

Bad panel?  Why would the picture look fine for a few seconds?  I do not have a spare of this particular panel so I can't try a swap.

Has anybody run into this before?
 

UPDATE: I went through my stash again and found a compatible screen on a Dell!  Connected it up, same thing. Comes on for a few seconds and shuts off.

At this point the only thing left is that they sold me a bad inverter. Does anyone have any other ideas or disagree with me?

I am at a loss.  I have replaced the inverter (twice), replaced the video cable (twice) and the replaced the screen.  The problem will not go away.  An external monitor stays on and works fine.   I have also tried two power supplies.  If I unplug the video cable from the motherboard (while the laptop is on) and plug it back in, the video comes on for a few seconds and goes black again.

I have been repairing laptops for several years and have not run into a problem like this.  Has anyone else?