Usually, I'd suspect the PSU when all 3 hash boards show 0 asics, but I saw you mention


In that case, I would say with at least a probability of =>90% that all hash boards have actually diead, Bitmain makes these gears terrible enough in the production phase, I would not be surprised if the repaired once come out even worse, that repair guy is in a bad mood and he rushes to fix the 100 hash boards he has in the basket next to him before 5 pm because he doesn't want to stay late, he quickly solders those chips and heatsinks using the terrible med-temp adhesive, assemble the miner and off he goes, and we all know there is probably no quality-control unit there, the "at best" just plug-in the fixture tool and count the number of chips and that's all about it.

If you have tried a different control board, a different PSU there is nothing else you can do, you will need to send the boards for repair, but since your first experience with Bitmain wasn't so great, you might want to find someone else to fix them.