I've tried to log in to this device by doing the following.
username: admin password: <none>
Maintainer credentials in the FortiExplorer console interface.
username: maintainer password: bcpb + serial number
Holding the reset button for varying lengths of time, and during boot.
Installing a newer firmware from ftp://pftpintl:F0rt1intl@support.fortinet.com
I've gleaned this information from random blogs. I can't find an actual manual, just spec sheets and sales pamphlets.