I assume there is no Tech near you??
We have 3 DATS still here and when we had to transfer a Job from 13 years ago, we had to fire them up and leave 'em on. Best to leave them run for a long time to get warmed up. Then try again. Also try power cycling a few times. They are finnicky things. Glad to see that tecnology go!
The manuals may very well be as rare as Rocking Horse Ca-ca, but you can but it online:
http://www.datrecorders.co.uk/d30.php
Good luck!