Does you E-04 beep (once) and flash the LED in the remote switch panel anytime power is initially applied?
After noticing that, I ran another check by leaving the airplane master switch on and tuned com radio to 121.50 and disconnected then reconnect the DIN plug, it beeped one time again and flashed the LED. No transmission heard on 121.50.
After noticing that, I ran another check by leaving the airplane master switch on and tuned com radio to 121.50 and disconnected then reconnect the DIN plug, it beeped one time again and flashed the LED. No transmission heard on 121.50.