Great news - I finally got the radio working again!

Saturday I spent most of the day at the hangar. First, I figured out where my cockpit brake leak is - both master cylinders are leaking where the sliding shaft comes out of them. I’ll order some new O-rings to fix that. I had replaced the original Buna-N O-rings with Viton ones that were compatible with automotive fluids, but I eventually decided to use a synthetic aviation fluid which would have been compatible with the original O-rings. The new O-rings were supposed to be compatible with the aviation fluid too, but I’ll switch back to the ones that Matco recommends as Buna-N is slightly softer than Viton, and that may make it better at sealing.

I pulled the cowling to do an engine inspection and to top up the brake fluid. I reinstalled the wheel pants and put the front seat back in. Then I did a short test flight, hoping to find that the radio was working. I could hear it in my handheld COM when I transmitted, but it was very broken. I was hoping that the high power transmitter was overpowering the handheld COM’s receiver at close range in the hangar, and that things would be fine when I was talking to stations a bit further away. But once I got flying I found that the radio was still not transmitting. :(

Late Sunday morning I attacked the problem from scratch. The intercom and COM 2 were working, so I knew that the wiring up to the intercom box was good. I used an ohmmeter to recheck the wiring from the intercom to COM 1, and everything was perfect. I tried bypassing the intercom, but that made no difference in the quality of reception on the handheld COM. I checked the resistance in the power and ground connections, and found that one of the power connections had a slightly high resistance between the radio tray and the fuse block. I cleaned the connection at the fuse block, which brought the resistance back down to a very low value. And, suddenly the handheld COM was picking up the transmissions loud and clear.

I pulled the aircraft out of the hangar and went flying. The radio appears to be working perfectly. Finally! I am so happy :)