Black screen fix possible?

This VAIO shows nothing on the screen. It works fine (including the touch panel) with an external monitor.

There's no faint picture either, so it's not just a backlight issue.

The screen connector shows no damage or corrosion.

Is it possible to isolate the problem on the screen's side or the mainboard?

A new screen is not available for purchase and it would probably also be prohibitely expensive to buy one. It would be cheaper to find another used laptop with a working screen.

I disaseembled the screen as per the instructions to see if there is an obvious fault, but all connectors looked fine and there was no corrosion or burned parts. The test points on the PCB measured the correct 5V. I suppose it's possible that there's a bad connection in one of the ribbon cables.