Roland Rhodes 760

Hi all, i’m new here and i hope to find help ! A friend of mine gave me a rhodes 760 with various problems and i would like to bring it back to life. Now leaving out the classic problem of keys with red glue and some buttons that don’t work, I would say that the main problem is that after turning it on, only the green display turns on and nothing else. I measured the output voltages from the power supply and they are correct. I found it without the backup battery which I replaced with a new one. Now my fear is that the operating system has been lost. I accept suggestions.