I, too, recently encountered a very vexing problem with the SL-40 radio. Garmin was of no help. I removed both the radio and antenna from my RV-12 and drove a long way to a radio shop for testing. As with you, both tested OK. After much tracing in bitter cold weather, and to make a long story short, I found the problem in the 3", L-shaped antenna connector where it attaches to the radio rack itself. A I recall, this part of the rack actually comes assembled from Vans. It is a "floating" attachment, so the radio can easily be racked & un-racked from the front.
Fortunately for me, once the "open" was located, my friend Jerry, who is a pilot, a builder and a very astute Navy-trained electronics guy, had the parts, the tools, the know-how and the willingness to re-build the part better than new for me in the nick of time to fly my cross-country in the '12 from Albany, NY, to Sebring, FL, and back for the Expo.
Hope this helps.
JRo
Fortunately for me, once the "open" was located, my friend Jerry, who is a pilot, a builder and a very astute Navy-trained electronics guy, had the parts, the tools, the know-how and the willingness to re-build the part better than new for me in the nick of time to fly my cross-country in the '12 from Albany, NY, to Sebring, FL, and back for the Expo.
Hope this helps.
JRo
