A first measurement of the voltages has shown that +9V and +5V are missing because of a broken fuse (1467). After ordering some spare parts – basically trying to get every component of the PCB – I replaced the fuse 1467 and also removed the transistors 7477 and 7478 of the same supply line. Testing has shown that they are not working correctly so they also got replaced.
Both voltage where working later on. Unfortunately the +12V are also missing and I traced the issue down to an undocumented 2.2Ohm fuse resistor right before C40 pin 8. The +12V powers the uProc board so the tape deck CPU got no power. A good indicator that the tape deck CPU stopped working is that the tape deck LCD display. In case of a malfunction it highlights all options. Furthermore the tape deck and play/pause/stop keys for the CD-Player are not working. The reason can be the missing 12V, a broken and undocumented 78×05 on the uProc board or a hanging or broken CPU (as seen at the first unit).
I have not got a 2.2Ohm fuse resistor so I used a 8Ohm which of course resulted into a voltage very close to the defined 12V. Since usually all voltages are too high this is a nice side effect.
Of course I replaced all capacitors and switched the 220V input to 240V as done with the first unit.
Pretty sure the power supply is one of the weak points of the sound machine. All three devices are facing issues and there are a lot of components that are getting really hot. The predefined voltages are all out of scope – e.g. 9.6V resulted in 13.8V and the 78×05 (7475) operates as a stove since it has to drop the voltage to 5V and burns the rest.