A320
Flight Crew Last 90 Days 105; Flight Crew Total 11000; Flight Crew Type 2600
Human-Machine Interface
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Other / Unknown
Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft
All three Radio Management Panels (RMPs) [radio] frequency windows went blank and we were unable to change radio frequencies. However; we were still able to communicate with ATC on last assigned radio frequency before windows went blank; then [did communicate] on Guard frequency; and also through relay with other aircraft. We were able to send and receive ACARS messages with Dispatch and Maintenance. Per Maintenance; we attempted a reset of all three RMPs and were able to use VHF-3 for radio frequency changes and communication. We were able to continue and land at ZZZ1.
Reporter stated the reset procedure for the Radio Management Unit RMPs suggested by Maintenance was to cycle the 'On-Off' power switch and wait five seconds between position selection; before returning to the 'On' position.  Only # 3 RMP was functional for frequency and communications after that on the A320.  The 'on guard' reference was the phrase they use when they monitor 121.5 on Comm # 2 and not meant as a reference to the 'guarded' NAV selection on the RMPs.  Maintenance later replaced the Audio Management Unit (AMU) and # 1 RMP.
We lost the ability to change frequencies on our radios. The [radio frequency] windows were blank. We were able to speak with ATC on Guard [frequency]. Through our ACARS data link we could communicate with Dispatch. After nearly exhausting all of our options to recover the ability to change frequencies; VHF-3 came back to life and the Captain was able to communicate normally. System malfunction.
Two pilots report all three Radio Management Panel (RMP) frequency display windows went blank in flight and they were unable to change radio frequencies on their A320 aircraft.