Oke, fixed it!!!!
It was the contrast! I've replaced the 10K adjustible resistor by two normal resistors and I've got image! A little dark, but I've got image! After that, I putt in another adjustible resistor and set the contract. Now, the image is just nice.
But a little backlight would be nice. According to the schematic, the pins 19 and 20 could not be connected, but I think they are. Copper tracks are running to the display. And they end at a place that could be the backlight.
When the display was still in the controller, it had a blacklight. Also, the PCB on which this display was connected, has 20V on the pins (that should not be connected

). I've put the display back in the controller and with the dispay connected, the is still 20V on those pins, so I think the backlight needs 20V to work.
I'm gonna hook the whole thing up again, but this time, it's gonna be the final hookup. I've found an old SUN classic1 would make a nice case for the display

Keep you informed.