Electrical noise

[McFly]

I started hearing an interment clicking sound in my headset about six flights ago. The clicking has NOT happened on every flight. On the last flight the clicking was very prominent and the tower said my transmissions were garbled. I assume the clicking and the garbled transmission are related but I am not positive. This is the only instance of a garbled transmission.



-A couple of the steam gauges twitch with in concert with the clicking.

-If I turn the radio off, I cannot hear the clicking through the intercom but the stream gauges still twitch.

-The clicking is NOT in sync with fuel pump strobes or anything else although the fuel pump may exaggerate it some.

-The clicking occurs with all equipment off except radio, intercom and the one Lightspeed EI (I just thought to turn off the EI and see if that tells me anything)

-I can reproduce the clicking during taxi but the engine must be running to reproduce.

-I also now hear a click when I turn on various equipment via a toggle switch .



The plane has a single point ground forest of tabs, Bob Knuckes three buss architecture. Data, antennae wires are run separately from power.



Under the panel I have tugged on wires/connections with the headsets on but no luck fining any loose connections. I am looking for suggestions on how to isolate the problem, trouble shoot the problem, or just theories. My plane did not have this issue for 125 hours, something must have changed but I don?t know what. Thanks.

[Mel]

Almost all problems like this turn out to be caused by a bad ground. "Remake" all grounds in the system and you will probably find the problem.

[elippse]

By "steam gauges" I assume you mean the engine monitor gauges such as Amps, Volts, Oil P, Oil T, EGT, CHT, etc. Do you have a good braid ground strap from the alternator case to the engine, and one from the engine to the firewall? Don't rely on alternator mounts to ground it!

[Geico266]

Originally Posted by Mel

Almost all problems like this turn out to be caused by a bad ground. "Remake" all grounds in the system and you will probably find the problem.

Beat me to it again Mel. Check your grounds on the equipment you suspect. Having them all bunched togeather is another suspect.

Something is causing the instruments to jump. Do they jump when the alternator is on line? Off line?

[McFly]

By "steam gauges" I assume you mean the engine monitor gauges

Yes, Vans engine gauges, fuel guages twitch the most and the right gauge more than the left. Others engine gauges don't seem to be affected.

Do you have a good braid ground strap from the alternator case to the engine

No strap on the alt and it might be something to try but it has not been an issue 125 hours.

Do they jump when the alternator is on line?

The alternator is online when this happens, I have not tried taking it offline.

Having them all bunched togeather is another suspect.

Could you please explain why this is suspect?

[Geico266]

Originally Posted by McFly

Could you please explain why this is suspect?

Too many grounds to one area. Try running an independant ground direct from the battery to the grounding cluster. If it helps then you know that is the problem.

[McFly]

Try running an independant ground direct from the battery to the grounding cluster

Thanks but I think I am covered here. On the cold side of the firewall I have the forrest of tabs where everything is grounded. The forrest of tabs is attached to the firewall by two monster brass bolts that extend to the hot side of the firewall. The battery and engine grounds are attached to these same brass bolts but on the hot side of the firewall.

[az_gila]

I vote for a bad regulator... especially since you say the clicks don't follow the fuel pump or strobes...

Something is switching, and if your 12 volt line is pulsing (the guages jumping......) clicks will happen....

Still could be a ground in the regulator circuitry though...

Do you have LED nav lights? If so, switch them off as a test...

gil A