The APU LED light turns blue when it detects any voltage (i.e., when you plug the APU into your computer's USB port). The light turns green when the internal APU computer has fully booted up. If the APU light stays blue, it may be for a variety of reasons. Trouble-shoot by trying the following, preferably in this order:

  1. The USB cable may be defective. Try a different USB cable.
  2. Try plugging the APU into a standard wall power socket using a USB adapter. If the APU boots to green then there is likely a problem with the computer's USB port or power supply.
  3. The computer's USB port may be insufficient or defective. 
    1. Check that you are using a USB 2 or 3 port, not a USB 1 port.
    2. Try a different port in the same computer (if there is one available) or try a USB port on a different computer.
    3. A defective port may be hardware or driver-related. If the APU turns green when using a different port or computer, you will need to use your own IT resources to fix the computer.
  4. Try booting the APU from a laptop on battery power, not plugged into the wall. If the APU boots to green, this may indicate a problem with the computer's power supply or mains power supply. If you suspect the host computer's power source is insufficient or defective, you may need to ask your IT support for assistance to trouble-shoot.
    1. Is the USB bus overloaded with too many devices?
    2. Is the USB power supply defective?
    3. Is the wall mains power excessively noisy? Significant digital noise getting into the APU USB power line can glitch the internal computer boot up. You may need a line conditioner.
  5. If suggestions 1-4 do not indicate where the problem lies, it's likely the APU is defective. Contact your distributor or Mimosa Acoustics to arrange servicing. Please ensure you return the APU and the USB cable.


Please let us know if you have any further trouble-shooting hints for this situation.