Bose A30 - Unwanted Noise

[thommy152]

I’ve got lemo Bose A20’s in our DA62. I get a soft buzzing sound from the headset after startup and the headset control module blinks orange. After I unplug the headsets and plug them back in, the buzz goes away and the control module light blinks green. I don’t have batteries installed in these headsets (I took the ones that came with them out because I didn’t think I needed them). I’m going to put batteries back in the headsets and see if it eliminates the buzzing sound after startup.

[Colin]

Instead of putting in batteries I wonder what would happen if you just completed the circuit. Tin foil?

[Rich]

Instead of putting in batteries I wonder what would happen if you just completed the circuit. Tin foil?

Assuming you could actually find tin foil (couldn't resist ), this wouldn't complete a circuit. It would short a circuit to zero ohms intended to have roughly 3 volts or mega ohms across it.

The Diamonds are wired in an interesting way. The LEMO circuit is tapped off the avionics bus. With the avionics master off, when you first energize the master (BAT side) the avionics bus is momentarily energized. (I can readily confirm this as the MB lights on my audio panel flash.) I found with my A20 that if there were batteries in it, this would cause its "on" light to come on and stay on. If there were no batteries in it the light would simply flash once. I note that my Zulus don't do this. There is a noticeable delay of a couple of seconds between turning on the avionics bus and the obvious silencing in the headset and the startup voice responses.

[dmloftus]

The evidence is that the A30 somehow requires extra power to "boot up" that the Diamond system, for whatever reason, won't supply, but is happy once it's been started. The batteries somehow fill the gap for the presumably short time required and then are not used. So far this is unique to this model headset.

Maybe an inrush current issue? I wonder if a decent sized capacitor would do the trick

[MarkO]

An interesting thing I have found. If I turn off the Electric Master switch after a flight, The standby instruments will turn off after 30 seconds as designed. However, if I leave my iPad plugged into the USB-C outlet, the standby instrument will not shut down - I must do it manually. When I next turn on the Electric Master switch, I get a warning that the Standby Instrument battery reserve could be less than 30 minutes. Is there a link between the standby instrument and the USB charger outlets?

[Rich]

Is there a link between the standby instrument and the USB charger outlets?

Yep. In the 62 both are connected directly to the main bus.

To elaborate, the USB adapters appear to be TA102 units. Apparently, they don't prevent voltage from feeding back from the iPad sufficient to fool the standby doodad into the thinking the master is still on but it needs to run on its backup battery.

[MarkO]

Thanks, Rich - I thought it must be something like that.

[Rich]

I wonder if this problem only happens in the Bose's if "auto on" is enabled. (It is specifically referred to in the writeup.) In which case perhaps it could be cleared by manually toggling the power button off and back on. Part of the equation is that power gets applied when turning on the avionics master. This means that lots of other things are also starting their boot-up sequence at the same time.

[steve_falconer]

I’ll test by turning off the Auto On and turning on manually without batteries installed. Let me know if you’d like me to do other user testing.

I’ve installed a new PS Engineering PMA450B audio panel to replace my Garmin GMA340 I’m testing this weekend, too. I wouldn’t think it’d matter for this, but bringing it up in case it does.

[steve_falconer]

Same behavior. Bose A30 does not turn on without batteries even with Auto On turned off. I’m still satisfied with the purchase since it extends my battery life substantially. I’ll report my Hobbs time when I finally change my batteries the first time. I started using the adapter with the Bose A30 about 5/23/23 and Hobbs of 5548.10. Current Hobbs is 5606.60 as of 8/13/23. Batteries are still strong.