When I do find a card combination that seems to work, it's not long before a card drops off and even a reboot or reseating the cards doesn't fix the problem. I've tried hundreds of card combinations, I pretty much have to rearrange them every time I restart. Which is like 20 times a day. If I don't, eventually only 1 or 2 cards will be left running. If any at all.
I know that behaviour very well (from a total of 7 units, so at least it's consistent...). What I did to mitigate this was to follow the steps posted by punin:
https://bitcointalk.org/index.php?topic=250249.msg3455392#msg3455392Although I waited 10-15 mins between the power off/power on in Solution B. Only waiting a short time resulted in cards still not hashing after the hard reset. Maybe there is some kind of fuse that needs to reset, which takes some time. Dunno. Nevertheless, the units are now hashing with 400++ most of the time. Also note that reseating the cards never changed/helped anything for me. Only a hard reset with the unit being turned off for at least 10 minutes got all cards back to hashing, with the config change proposed by punin (turn off auto-tuning) helped to keep them hashing...