Hi,
Thanks much for your answers. Yes, I saw the thing with the voltage adjustment but no idea how to do it. Maybe I find a hint in the T1 user manual.
The blue LED is working fine, haven't tried a reset yet though. I also rechecked the connections. Everything as it should I guess. What really bothers me is that I have no way to check if the screen was sent to me in a workable state. My guess is that is is really not so easy to adjust the voltage as Booxtor wrote. Instead of saving money I will be spending more...

Should have listened to Booxtor and send it in directly