701C Booting Problem

[hjanzen]

Hello,
Just now when I started my beloved 701C, as soon as anything appears on the screen, starting from the memory count, the picture starts rotating vertically continiously.
It does not make any difference if I restart the laptop f.i. while depressing F1 (set up appears, rotating) or safe mode, battery mode or AC adapter. All the same.
Your help in resolving this serious problem is much appreciated.

I have in the meantime connected an external monitor via the portreplicator. Perfect image!
The original display keeps rotating when I toggle between the two with Fn F7.
Thus...
Inverter, backlight , cable connection ???