ELT noise

[cbmontgo]

I have a little bit of a strange ELT issue.

When I turn on the master switch, the ELT starts making noise (the classic ELT sound), coming from the unit itself. It is not sending out an ELT signal over 121.5 though.

I've hit the reset button, turned it on and off, and nothing stops the noise. Any ideas on the cause? The batteries were just replaced at the last annual I believe.

Here is the unit:

 

[Dan Thomas]

Not the ELT. It's the strobe light. Its powerpack makes a similar noise. Likely a bad ground in that circuit.

 

[Warlock]

Yep the rotating beacon will produce the noise…turn it off and see if it stops…

 

[cbmontgo]

Thanks, guys!

 

[Dan Thomas]

Yep the rotating beacon will produce the noise…turn it off and see if it stops…

Rotating beacons just made motor noise, which didn't have a regular frequency warble. The strobe's powerpack has an oscillator in it that takes the 14 VDC, breaks it up into an AC signal, and runs it though a transformer to get the high voltage needed for the xenon strobe bulb. It charges a capacitor for this, and as the capacitor fills the frequency goes up until it discharges, and then starts again.