So maybe I'm going to show just how green I am at this stuff but I took a used Fostex 812 recording mixer out of the box, that was consigned to me by a widow, (so there is no one to ask)and low and behold there is no power cord or on off switch. There is however a 15 pin computer connection in the lower left hand corner that seems to provide no power to it when hooked to a midi controller, the only thing I could try while stupidly staring at the back of the damn thing. Is it safe to assume the parts were pirated off of the thing or does 15 pin in fact supply power. There may be a power supply in the attic yet to found but I'm baffled what to connect it to if the 15 pin isn't the place because there isn't anywhere else and when I pulled the back cover there aren't even wires to hook up a switch.
I found the manual for the unit online, and it appears to have a standard attached AC power cord (like the kind that comes out of a lamp or a toaster) coming out of the upper right corner if you're facing the back of the unit. Here's the link to that page in the manual:https://www.manualslib.com/manual/53280/Fostex-812.html?page=5#manual
Since it isn't there, it must have gotten pulled out somehow. It probably wouldn't be too expensive to get that replaced if you could find a qualified repair shop.