/vr/ - Retro Games

I'm a programmer and I want to program for arcade hardware, or at least make romhacks and stuff more than simple graphics and text changes
Ive done programming and romhacking for nes and genesis before and it wasn't too bad due to there being such an abundance of information and tools, but arcade hardware is a whole other beast and yet i see people who are experts at this stuff but no information or tutorials anywhere

Where do I even begin to learn what any of this shit means, pic related is my attempt at identifying parts of a pcb. In archives I see somebody reccomending MIT 6.004 but where do I go from there, MIT 6.111 seems more relevant as it mentions PALs and flip flops (which i think those little things on the pcb might be) but I can't find the course material anywhere online

I also found this book that seems somewhat relevant but it's from the 1970s and meant for fucking discrete logic games
http://discrete.mameworld.info/Docs/VGLvol1.pdf
why would they still be using this stuff in arcade hardware (but not console hardware) in the 90s when processors exist (again i'm a brainlet so sorry if i'm asking to be spoonfed and the answers to all these questions are obvious)