Bomb 15 is related to polygon (the part behind the lenses if you open the top cover) or with the laser and all that it involves. In my experience try cleaning first all the optics area, starting from the polygon. You just need an air blower and maybe a soft brush, and rice paper (used to clean camera lenses). Don't remove any screw or any part if you don't know what it does and how to do it, it's very easy to have a uncalibrated system just turning a screw, specially those who have painting DON'T TOUCH THEM!!!. Bomb 15 means the laser is not reaching in a right way to a sensor (SOL), it could be caused by dust, that's why to clean it first. A second test could be increasing the laser exposure (you do that at the RIP, do it in steps of 5) it will not fix the problem, just give us some clues, because if you increase the laser "power" it could reach the SOL in a "right way", but increases the film density too.
