Night time, back to the radio hiss problem...
FG (I) radio board:
Modified FGII radio board:
Side by side picture:
I can see the new one has more components near the white connector, all the other components are the same - but I assume the custom 16 bit CPU has different programming. I wonder if it detects the board by the components on it? Maybe removing some/all of the different ones will make it work better?!