Please detail what I should disconnect to isolate a single board to try and determine which is giving me the LIBUSB error.
Nearly a week has passed and not one response to my emails to hashfast regarding my faulty units.
Use the latest cgminer and firmware. Run at 550Mhz when troubleshooting.
Take pictures of the original config before you change anything so you can put it back.
The ribbon cable is used to link the chain.
Disconnect all the ribbon cables to isolate a board.
Use two PCIE power cables from the same PSU for an isolated board.
Connect the power cable (white connector) from the board to its PSU, if it is not already.
Connect the USB cable (black connector) to the board, but make sure the thick black wire is closest to the ASIC (red wire farthest from ASIC).
Try running the boards in pairs (sets of two). If that works, add the third back in. Some boards don't like to the be the master (first board in chain) so try boards in different orders.