Hello, I’m new here, anyway I got a question. I have a MG-1 and some of the keys don’t work, when I’m in the “keyed” mode in tone sources, the following keys do not work: 1st and 2nd G notes, 1st c note and the 1st F sharp, the 2nd Fsharp cuts in and out, and the 1st C sharp. How can I repair/clean this problem ? Thanks in advance for anyones help. 
Sounds like bad divider chips (mm5823)
It may need a tech and one that can get these somewhat rare ICs.