I did some audio testings to verify that I really needed to clean everything. So I started my usual restoration process.
1. Taking everything apart
2. Cleaned all the potentiometers (desoldering, open, ipa, close, test, soldering)
3. Cleaned all the switches including the rotary (desoldering, open, ipa, close, test, soldering)
4. Cleaned the keyboard
It´s not only done by washing the keys. Rather it's a refurbishing process of the contact-strips. In this first picture you can see a worn out contact...