There should be 4 little lightbulbs. Maybe like on a christmas tree if one goes out or are broken the whole thing shuts down. Id send it back cause theres no way to fix that that I know of. No troubleshoot or anything cause I believe the illuminator is not something the user has control over .
My first guess would be a bad internal electrical connection to the LED's. If you can't exchange it, I would attempt to dismantle it and check all the connections including any possible cold solder joints on the LED pcb. Good Luck!