This is an RMI Electra 300A, but the service manual I found is for a 368x, so this method should work for all RMI Electra pianos. Probably not true though for Rocksichord and even earlier models like the RMI Lark and Explorer. This video shows how to get it into tune, and I also talk about hum and sustain problems.

Service manual download: http://dannix.net/lib/guitar/rmi-elec...

This is an "electronic" piano that not many people know about compared to a Rhodes or Wurlizter electric piano, but in the early 70s it was commonly used by touring musicians who didn't want to travel with a full piano. However there are some notable exceptions of when an RMI was used in the recording studio: "Dream On" by Aerosmith, "Hello, I Love You" by the Doors, and "Right Place, Wrong Time" by Dr. John, among many others.