It seems tinned but wasn't a few minutes before I took the picture. In short, the small black locking bar from the connector broke at one end, and the cable wasn't safetened any more correctly and could move away. It resulted by the backlight being on but no image, or image but with the wrong colors (most probably due to misalignment of the flat cable and the connector). I tried to replace the cable back in place, while watching the screen to see if the colors were going back to normal, but I guess a short appeared and the screen went black. When I removed the ribbon cable I saw this "tinned" aspect on the right side of the connector, and my guess is there was a short on this part (VCC for backlight??) that melted the connector and/or cable?
I'm away from home for a couple of days and won't be able to check anything sooner, I just fear I've broken the whole scope...