Typically the maintenance manual has wiring diagrams as well as a trouble shooting section that advises you where to look for what voltage.
First a note that Bridgeport had a service report that negated a warranty on a machine running on a phase converter.
Now check power in, all three phases. Next check the 24 VDC power supplies. The TNC2500 had a 24VDC supply that fed the control logic power supply. There was another one that ran the relays. If no power out, is there power going into these? If not follow it back.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)