Yamaha CS-30 Synthesizer Repair Service. This synthesizer was delivered to me by another repair shop. Quote: "Our technician ... doesn't know about synthesizers. Our customer asked that we send you the device ..."
The Yamaha CS-30 synthesizer only made "clicks". As if the envelope and audio output are working, but the oscillator (s) are not working properly. My guess was correct. There were a few defective solder joints that were quickly found and fixed. After that, the CS-30 ran again. But there were a few other minor problems.
The Yamaha CS-30's sequencer was only half running. A defective 4016 logic ic was responsible for this. I exchanged this and soldered in a socket directly. Now the synth was running again. Now there was still a lot of cleaning work, as all potentiometers and switches were corroded and therefore did not function properly (fluctuations, instability, cracking, scratching, etc.).