Spend the day checking all the radio system - took a while as it is the most complicated system in the plane. In the end I found 2 faults. One soldered connection had failed - probable from being pulled too hard with one of the many panel installs and removal ...
The other fault was with the headset jacks. I wired them exactly as specified by MicroAir but they still didn't work. Ed Smith happened to drop by so he ran some tests and advised that there are two types of headset plugs commonly in use. The set I had were the old style and didn't match the jack wiring. He did some quick thinking and designed some wiring that would accommodate both jack styles. An hour or so later and the jacks will take both styles of headsets and work properly. Handy having Ed drop by! One problem crossed off the list ...
