Try these solutions:
1. Check all loudspeaker connections before attempting to switch the unit out of Standby
There may be a short circuit between the loudspeaker terminals.
During power up from Standby CAP5 performs a check on the loudspeaker terminals to see if a short across the terminals has been accidentally introduced. If the resistance measured across the loudspeaker terminals is too low the unit will stay in Standby mode until the fault has been removed and Power up is re-attempted.
2. Check the specifications of your speakers to ensure that they are compatible with the CXA
Both amplifiers can be used with speakers with an impedance of between 4 and 8 Ohms.
The CXA61 outputs 60W RMS into 8 Ohms and 90W RMS into 4 Ohms, while the CXA81/81 Mk II outputs 80W RMS into 8 Ohms and 120W RMS into 4 Ohms.
If your connected speakers fall outside of these specifications, then this could also be a reason for CAP5 protection being activated.