Yesterday evening local RV-7A builder Jim M. came by the airport to help me with radio functional checks. He sat by the radio in the Smiths Falls Flying Club and responded to a whole series of radio checks. I confirmed that all transmissions on COM 1 (GNS 430W) were carrier only, from front and rear seat, with two different head sets. COM 2 (MicroAir 760) worked, but I discovered that there is an issue with the COM 1/COM 2 selector toggle switch on the audio panel. This switch seems to be intermittent in the COM 2 position. It works properly, if I push it slightly upwards while transmitting. I’ll need to send the PMA 4000 back to PS Engineering some time to get that fixed.

Now that I had a better idea on what worked and what didn’t work, I could narrow down the list of possible causes. The COM 1 Mic Audio high and low wires between the audio panel and the GNS 430W were the prime candidates.

I took some comp time this afternoon and zipped out to the airport to look for the COM 1 problem. I pulled the GNS 430W out of its tray, and disconnected the wiring harness from the back of the audio panel. Some probing with an ohmmeter showed that the COM 1 Mic Audio Lo connection between audio panel and GNS 430W was bad. Some more probing around suggested an intermittent failure somewhere between the DB-25 connector at the audio panel and a Molex connector that joined the audio panel wiring harness to the GNS 430W harness.

I cut a whole bunch of wire ties and managed to free up enough slack so I had reasonable access to the DB-25 audio panel connector while sitting in the front seat. Unfortunately the connector is the type with the wires soldered to the pins, and my soldering skills are nowhere close to good enough to work with stuff this small. But, each of the 18 wires on the connector has a pretty long pigtail before it disappears into the shielded cables. So, I think the best fix is to convert to a connector with individually removable machined pins crimped onto the wires. I’ll completely replace the three wire cable that contains the intermittent connection and crimp new pins on the ends of all the other wires. I need to acquire some more machined pins and a length of three wire shielded cable. I should be able to get that next week, and I hope to rewire the bad connector the weekend of 12-13 March.