I installed the 5w laser and disabled the fan entirely, replacing it with the power cable from the laser. When I plug it in, the laser is on full power even with the fan speed set to 0. I tried to flash the laser firmware but it leaves my screen blank and nothing happens. I flashed the new Marlin 2.0 firmware but that gives me no options either. Any help would be greatly appreciated.
Marlin controls the signal from the controllable fan to control the laser, which is invalid after changing the fan speed on the screen, and cannot change the laser power. With fan control, the power can only be 100%, which means that you cannot adjust the power, only the engraving speed.
However, you can use the laser box with the laser and printer together, so you can control the power and have more types of engraving and better quality
The link of laser box: