On May 29, 6:30 am, Steve - KDMW wrote:
...
They indicated that they did an exact wire-for-wire swap with the COM
120. The intercom volume drops as soon as you turn the SL40 on. You
don't have to be transmitting or receiving for the problem to occur.

Steve

When the SL40 is powered up, the feedback around its audio output
amplifier becomes active, creating a very low- output impedance. If
this is paralled with something it shouldn't be, then this is what
caused the audio level to drop.

This leads me to believe that the headphone COM120 output was NOT
wired to the isolated summing input on the audio switching panel as it
should have been. AFIK, Narco products have an internal resistor in
series with the headphone output, which might prevent the volume drop
even as wired.

A half-assed fix would be to insert a series 100 Ohm resistor in the
wire coming from the SL40 headphone output. A better fix would be to
trace out where that wire actually goes...