In my case a spider had made its home in the lens opening in the drum which caused the unit to throw a 3000 error code. Removed the web with a pick and reassembled. That was the issue. Not kidding.
Folks, for an error 3000 (laser/lidar) issue check that the openings for both the laser and receiving lens are clear of obstructions. Spiders are known to climb into one or both ports on the drum and make webs/egg sacs in there. Remove with a toothpick or similar being careful not to damage the lens/laser. Not kidding. The belt and motor were fine; the web just obscured the lens opening in the drum.
As mentioned, some 3g phones there is a small metal clip holding down the camera (held in place by the screw there). Be sure it doesn't fly out or fall into the phone workings. Fine point tweezers would help here, to take it out and to put back in place during re-assembly.