OK, one last question. How long has this exact radio stack (radio,
intercom, headset, etc.) been in the airplane, and have you ever witnessed
it working correctly? Has anything ELSE electrical in the airplane changed
between the time it worked correctly and the present time?

I'm going to go out on a bodacious limb and say that there is some vital
connection between your radio light dimmer and your PTT line. THere should
be absolutely no connection between the two.

Jim




"Jonathan Goodish" wrote in message
...
In article ,
"RST Engineering" wrote:

1. THe nav lights (you are talking about the ones on the wingtips --
red,
green, white in the back) are working just fine. What would this have to
do
with the problem?

Nothing, other than the fact that they are activated by the same switch.
in the Cherokee.

The same switch as what? Are you saying that by turning the radio lights
pot from off to just barely on (switch snap) also turns on the nav lights?





2. The internal instrument lights are working just fine. I'm presuming
what you are telling me is that if you connect a wire directly from the
+12
supply to the instrument lights then they illuminate at the proper level.
You DID take the dimmer out of the circuit for this test, didn't you?

No. With the dimmer in, the instrument lights (radio backlights)
illuminate and dim just fine.

OK, let's agree on some terminology so we don't keep running down the same
rabbit path. Does the SAME dimmer run the instrument (post) lights as the
radio lights? If not, let's have an INSTRUMENT LIGHT dimmer and a RADIO
LIGHT dimmer.





3. WHen you turn up the dimmer potentiometer so that the "instrument
lights" (do you mean the radio backlights or do you have some sort of
lighting system on the gyros?) then you get a certain amount of noise,
mainly in the headsets but some in the speaker as well.

I have two circuits, panel lights and the radio backlights. The circuit
in question is the radio backlights.

You are correct, when I turn the pot so that the radio backlights
illuminate, I get noise that escalates in volume as I turn the lights
up. The lights appear to illuminate normally. When I get more than a
little current in circuit, the intercom squelches the mics on all
positions.

Squelching the microphones turn them off. Are you saying that the radio
dimmer turns ALL the microphones off when the lights start to get bright?


6. You said that you can't hear radio transmissions, yet in a subsequent
post you said that you CAN hear radio transmissions. Which is it?

I can hear transmissions at all times, even when the buzzing is present
through the intercom when the radio backlights are at full brightness.



8. I don't suppose there is a chance in hell that you have a schematic
of
the dimmer?

Yes, I do.



9. What sort of test equipment can we presume as we toddle down the
fixit
trail? A handheld AM broadcast band receiver is a hell of a good buzz
detector.

I have an AM radio and a digital VOM and that's about it at the moment.