no voltage between the two big buss bars. Shouldn't I be getting 14-21V at those bars?
Not really, if there is no load-demand the PSU will only be outputting 12V to supply the control board which powers the fans, but that doesn't mean your PSU is good, it's likely dead if all 3 hash boards stopped showing, maybe post some screenshots and the kernel log as they usually give enough information to diagnose the miner's issues.