Due to an info on wikipedia, about the electronic music pioneer Robert Rental (1952-2000) and attributed to Mutant Sounds blog, a previously unreleased demo tape from 1979 has quite recently surfaced on the net. The music cassette release was titled "Mental Detentions".
A link to download the release can be found on mutant sounds.
:: mutant sounds
:: Robert Rental at wikipedia
:: discogs
:: mutant sounds
:: Robert Rental at wikipedia
:: discogs