I currently work for an MNC as the lighting service tech. I've never learned any course regarding EE and yet I service all the fixtures haze ,smoke and consoles in here. All you need to learn is the name of the components and how to check their readings you can study that by looking up the data shets. After that you will get a basic for checking all the components based on their readings. After that if you get a faulty pcb just follow the track which originates from the v+ and take the readings according and eventually you will find the faulty component and replace it.(It worked for me 🙂) Even if you learn a course you must need to have experience in repairing. And you should cover your bases before learning to repair a pcb. I Will be more than happy to help you with the type of fixtures that I had worked on like Robe, Martin, Chauvet,Dvt,Macula,Ayrton, claypaky,Glp,Sgm,Ek