Here is an interesting blog of calibrating an old synthesizer. It's not allways a direct path, instead it usually takes many twists to accomplish. Michael Fuchs decided to calibrate his CS-80 synth and it took him almost 4 weeks to accomplish this. He documented the whole process in this blog (https://mfoxhd.blogspot.com/). If you are interested in repairing/calibrating old synths I recommend you to read this 12-part document. It's an interesting and educational story!