To start down the road of reverse-engineering the galvo driver and making a much better one, I've taken pictures of the PCB and carefully gone over the traces in Photoshop. I found that the parts were obscuring the traces so I removed them and took more pictures.

Getting pictures with good contrast was trickier than I expected. First I tried taking a picture in regular room lighting but it was too hard to tell the traces apart from the substrate. So then I took a picture with backlighting in a dark room, but that caused the features on the opposite side of the board to obscure the side facing me. The magic combination was dim front-lighting and strong back-lighting. Not the best quality, but good enough.

Several hours after getting those pictures...

I loaded the images I had taken into Photoshop (Gimp works too) and traced over them. First step was to flatten and align them, which I did using the perspective crop tool. Then in separate layers I traced out the top copper, bottom copper, and vias with the paint brush tool. It might have been possible to use thresholding or edge detection to get the traces faster, but I wanted to be sure they were correct, wanted to have to examine every millimeter of the board, and just enjoyed tracing out the PCB while listening to electrical engineering lectures on Youtube.

And then several hours after that...

I filled in the parts using a vector editing program (Illustrator, but Inkscape could do the same). Lots of extra work but I wanted to reduce the opportunity for error when making the schematic and also start getting a sense of how the drivers work. Also it's useful documentation, because now I can go back and make images only containing parts for particular subsystems of the circuit.

Next up: working out a simplified schematic of one driver (one half of the board).