On Jun 3, 2:54 am, mikem wrote:
On Jun 1, 7:35 pm, mikem wrote:

On Jun 1, 5:03 pm, Steve - KDMW wrote:

Another tidbit of info. The intercom comes back to normal if the
Garmin radio is on and not selected. It doesn't load down the intercom
simply by virtue of being on, it has to be on and selected.

...

Another thought: If the summing resistor normally in series with COM2
input inside the Audio Panel has been removed or shorted out by some
strapping jumper, then you would get this behavior. I'm not familiar
with your audio panel, but each input should have a series resistor
between the input pin and the summing junction (op amp input). If for
whatever reason, this resistor is missing, the SL40's low output
impedance would upset the balance at the summing junction. Opening the
COM2 switch would make the problem go away. If the old COM that was
removed had some resistance in series with its output, then it would
NOT have upset the balance...

The KA-134 has an open chassis. I could take a look. I'll trace the
solder track from pin D. If I don't find anything, I'll try a 100-ohm
resistor on the Com 2 input.