X200 tablet only displays on external monitor

[xyz]

I have been playing around with a couple of tablets
swapping screens,

I have ended up with one that only works with an external monitor

Was initially no display

Replaced fuse f7 and it was now showing a lit up blackdisplay

Is there anything else to check
or have a I shorted the the graphics card a couple of times I did not remove all power from the unit.

what is verified..

Lcd is 100% ok
lcd cable is ok
Lcd adapter going to mother board if ok..

Any ideas