Hello Colleague!, From Argentina I answer you, although I am not a technical specialist in electronics, I have studied and I continue doing it because I am passionate about electronics. As for your question, I also have a "relic" of National SG-K200 equipment, similar to yours, and I have never been able to find an electronic map of it, to the point that I wanted to compulse other (used) equipment and neither I found, so I decided to reach out, and gradually study it and try to compose it. My advice is that if you want as a relic, slowly disarm it and replace the defective parts (capacitors, resistors, etc.), start at the source, and follow the path; these teams carry several power transistors, which generally deteriorate with time and heat; then always follow the logical path and may God help us !!!! If in case I find the map, I will let you know.- A big hug!!!