I can say with large lots of units, it takes more than a few days to weed out the bad ones. If they are just plain dead that *is* pretty easy to troubleshoot, isolate, and prepare for warranty repair. But most of my faulty units have been intermittent out of box, quickly deteriorating from that state to only one hashing board will be online. It takes alot of monitoring to find these in a large lot. In addition I reseated the faulty hashing boards to try to wake them up again, and was successful half of the time. But this step requires monitoring all over again to check the results of your work. It takes a good 24 hours or more of hashing to get a good reliable reading.

Basically all I am saying here, is it took me a whole month to weed out the bad hardware for warranty repair.