Hello everyone. My first post. I have a Kenwood 4230BT, customer said that he tried to do a firmware update, the unit hang and he removed the power from the battery. Hence, the unit is now bricked. Black screen, no response from buttons. Some models have a pre-boot mode, but I don't know if this one does. Or some key combination. If someone can point me to the right direction on how to recover this unit`s firmware , I would gladly appriciate it. Thank you.