If any amplifier fault should occur (hard or soft faults), the fault code and fault description is shown. The most common fault is Soft Fault 14. You probably have the wrong antenne connected. The amplifier switches from Operate to Standby. Push the Reset Button to switch back in to Operate mode. All Alpha 87A Faults codes are listed here.
Be sure not to ignore any amplifier fault!! Please refer always to your Alpha 87A operating manual!
The last eight amplifier soft and eight hard faults can always be queried under the Help menu, even when the amplifier is off: