It seems that the R.A.M. company is no more (went out of business or was acquired). This mixer was also on the market before electronic documents were widely available. I honestly think you are out of luck, unless you could stumble across a manual on eBay.
You might sign-up to the forum linked above and seek a current owner of a RM16 to see if they have a manual. If you could locate such a person, they might make you a copy and send to you.