www.makemkv.com

Hi, I've had a working BU40N drive on DE firmware for a few months, but it suddenly stopped spinning up discs and would just appear to spin them slowly a few times and then quit. I tried to flash it to stock and then back to 1.04.MK and back to 1.00DE, but midway through flashing it to stock it failed and refused to do anything further.
Upon reboot it reports its firmware version as BOOT and has a different SVC code than before, NS50 instead of BU40, and neither the stock flasher nor the SDF one one seems to do anything. Attempting to use the SDF flasher to read and dump the firmware shows a progress bar but doesn't actually dump a file. I'm pretty tech savvy, but if it's not possible through any way to fix this, let me know and I'll just make a new one. Regardless, thank you guys again for the documentation to make this one, even if it didn't last very long.

Try the factory firmware, it has worked for me
https://www.lg.com/us/support/product/lg-BU40N.AVAA10B

That's what I initially did to fix it, version 1.04 failed mid way through, putting it in this state. I've had it work before, so I'm not familiar with what's usually done if and when that happens. Trying to run it now doesn't work due to it detecting the SVC code wrong. If anyone knows that it *is* fixable with a reasonable amount of effort, let me know soon or I'll just send it back and report the BD drivehead as defective, since it most likely is and the only way to absolutely confirm that is to have it work again, which is what I was attempting to test before the official firmware screwed it for some reason.

Your problem was you tried to go from 1.04 to 1.00 if you read the uhd guide you would know that's not possible or recommend

I did read the guide, as far as I could tell there isn't anything wrong with using 1.00DE on an originally 1.04, only that you must flash 1.03MK first, if that's incorrect then my understanding is mistaken. I went from stock 1.04 to 1.03MK then to 1.00DE. I did that somewhere around a month ago and it had been working well until now, was that a fluke?
These problems started when the drive suddenly wouldn't spin up discs and would not detect them even though it had a few minutes ago, so I tried flashing it back to stock intending to repeat the process, and that flash failed halfway through, resulting in this upon reboot.