You will know if the 75 All Road handset is connected to the black box via the ‘LNK’ icon at the upper right corner of the Handset LCD.  If ‘LNK’ has a line through it, this tells you connection is lost. If ‘LNK’ appears and the handset screen is frozen or not responding, turn off the handset and plug it into the black box directly to re-establish connection.  Power the handset ON and you should see ‘LNK’ appear on the display (showing you are reconnected).