It is more likely that the USB is screwed up but there is an ocassional thing that is power supply related. So try following this sequence in powering the rig up again up:
(1) Remove 12V power and ideally unplug all USB leads at Cairnsmore1s. If you happen to have a USB hub with a switch for on/off that can work as well as unplugging if it properly removes USB power. Do check that it does remove power some don't do this properly. Basically we want the boards to be fully de-powered before starting. This is also the only way also to reset the USB controller if it gets upset by sometime and we have seen that a few times.
(2) Power 12V and Controller LED is flashing on all boards and each FPGA section is powered and configured - LEDs bright.
(3) If you don't get Controller and section LEDs doing the right things modify the power up of the 12V by doing an initial momentary switch on then off and on again.
(4) Plug back in USB leads either one by one or use the hub switch if you have one.
(5) Make sure you leave enough time for USB to enumerate before firing up mining software and better still check USB ports/COMs are all correct and present in the host.
When using master/slave in Controller 1.5 it is important that both boards of the pair power up together otherwise one may fail to start up and that is only an issue for master/slave usage. We are going to try and improve the Controller to either remove, or reduce, this powering up dependence but that might be a few weeks before we have the time to do that.
Ok, didn't try exactly that yet, but I always wait some time before testing. USB on host enumerated, correct and presented. I can do a request using kano's python script. I can see during request flashing lights on pair of FPGA's (so they handling incoming request?), I can see even green light on one of them (got nonce?), but no response on host after timeout (70%) or wrong response (30%).
Boards failing after complete reset, when no power at all, even no usb powert to them. Tried starting boards then host, host then boards - no changes. With or without usb connected. Controller red light blinking pretty fast all time when PSU turned on and power cables connected.
So, for now, to resolve this issue, I power down slave, than master. Then power up slave/master or master/slave doesn'y matter.
Usually failing 1-3 boards out of 12, usually different.
Also, I received my boards with controller 1.5, but 6 of 12 didn't work in master/slave - FPGA-s LEDs was red after board boots. So, I flashed controller, it seems to be resolved for now.
Hmmm... How much power each board requires during start process? Have not measure voltage output on PSU during start.