HM-56 Capacitor Replacement -Technical Bulletin AM-081904-EU11
Electrolytic Capacitor replacement
An age-related failure of the HM56/56A microphone, causing the radio to remain in TX mode when the mic is connected, is failure of the electrolytic capacitors on the microphone circuit board. Generally, replacing all 5 capacitors on the board repairs the problem and allows the microphone to work properly again. This repair does not guarantee performance.
The 5 capacitors on the board are labeled as C3, C5, C7, C13 and C14. They can be ordered from the Icom parts department using the following part numbers:
Icom America Tech support 8/19/04