Korg 707
I received this instrument with a note stating that it had lost its original presets and produced only some strange beeping sounds instead. There was also no way to restore the original sounds.
The „beeping” was most likely the result of a previous replacement of the CR2032 battery that maintains the RAM memory. After a quick diagnosis, I found that the MIDI input interface was not working. The faulty component responsible for the problem was the input optocoupler — quite a strange failure, actually.
After repairing the MIDI interface, I restored the original presets. Since the instrument was already in the workshop, I also replaced all the control-panel microswitches, as some of them were working with great difficulty. I also replaced the electrolytic capacitors located around the microprocessor and in the RESET circuit.
