Update: Took all the tools in creation to the airfield today. Found that the headset jack plug sockets are fitted into an aluminium box section, which is itself pop rivetted to the airframe. Of course the only two tools I didn’t take with me were the electric drill and the pop rivetter – sod’s law!
Anyway, we all seem to agree that the crackling is a loose or dry solder joint or one that is shorting to where it shouldn’t.
Today we flew circuits for 15 mins and all was quiet, landed and then flew again. Approximately 15 mins later whilst flying the dreaded crackling occurred with “TX” flickering in time on the radio display. This suggests that the problem could be heat induced (taking time to get to the temperature that the fault likes). Again, during flight we turned the radio off, strobe off and transponder off – no change. Removing either P1 or P2 heatset jack plugs whilst in flight seem to cure the problem but only for a short time and then starts again.
After landing we realized we had not turned off the avionics isolator switch in flight so did a few circuits for the test. The first 10 mins were quiet then on the final down-wing leg the crackling started again. We then turned the radio off and also the avionics isolator switch but could still hear the crackling in our headsets.
We conclude so far (cautiously) that with the avionics all off and only the master switch on (engine running or not), the fault seems to be within the intercomm and/or the jack plug sockets as nothing else is switched on.
Next trip to the airfield is planned for wednesday 16 July. Will keep you posted.
Richard