I have a S4 B1 and S4 B2. The S4 B1 is working great but the new B2 that i got in a couple weeks ago worked great for the first few days now I cant get it to hash more than a couple hours. The box would stop hashing but it would stay on, the fans on with a blank (but lit) LCD screen.
I re-seated the SD card and it worked for about 10 hours and started doing the same thing. It works if I turn the power off and turn it back on, but only hashes for a couple hours.
I got a new SD card and flashed the image from the original SD and that worked for a few hours and then it stopped hashing.
I emailed tech support and they sent me an image that I flashed to the new SD card and the same issue.
This is frustrating! I know it works, I just dont understand why it keeps stopping.
Have you tried different pools?
Increase the voltage slightly and/or underclock. Disconnect one or two boards. Try to isolate the problem, whether it's a bad board, cable, controller, PSU etc.
I have one that is doing that sometimes too. You know what I think it is? I think the vibrations from a stack of 6 S4's (this on is in the middle) is slightly shaking the SD card and causing the cgminer to stop.