Disc drive won’t read discs, just pulses.

Have you made sure all the wires are working right take a multi meter and pi it into Continuity mode and then check the ends match the ribbon cable End-to-end With the corresponding pads on each side then make sure that you test each individual pad 1 by 1 That way you can tell whether or not you have a short in the actual wiring itself ribbon cables are very delicate and can easily break or overheating of the device it is can cause them to fry. If that doesn't work then again in the same mode test the processing chips in charge of encoding the video in the motherboard because if you are not getting the disk read and have changed out the laser diode the the problem is on the motherboard itself. Hope that helps!!