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New noise in headset

uk_figs

Well Known Member
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Unusual noise/crackling in the headset today somewhat tied to engine RPM, disappears when intercom turned off (PM3000). Basically unusually noisy background and then specific regular beating crackle noise when RPM hits around 1300 and goes away at 1500 or higher. Never happened before and nothing changed on the aircraft recently. Was fine flying earlier in the week.
0-360 with slick mags.
I could fly without the intercom but all the aural warnings are routed though it.
Any ideas about where to start troubleshooting or things to check?
Thanks
Figs
 
Unusual noise/crackling in the headset today somewhat tied to engine RPM, disappears when intercom turned off (PM3000). Basically unusually noisy background and then specific regular beating crackle noise when RPM hits around 1300 and goes away at 1500 or higher. Never happened before and nothing changed on the aircraft recently. Was fine flying earlier in the week.
0-360 with slick mags.
I could fly without the intercom but all the aural warnings are routed though it.
Any ideas about where to start troubleshooting or things to check?
Thanks
Figs
Try turning off one of your mags to see if it's related to spark plug wires - I've seen this happen.
 
Try turning off one of your mags to see if it's related to spark plug wires - I've seen this happen.

Not the mags, same on both mags, rhythmic noise occurs as RPM transitions through 1200-1250 rpm. Not there when PS3000 turned off or when PS3000 ISO is selected so appears to be intercom circuit related. Maybe vibration related like a loose connection? Squelch control does not appear to help.

Not a huge deal except for the loss of SL30 and Aera 760 aural alerts when the intercom is switched off. Probably should have ganged all the audio inputs to pin 17 which is active even with the PS3000 turned off.
Figs
 
Check AC content of your alternator output. or Turn off field power.

?? I had a ticking sound -it turned out to be a less than tight nut on the mag post.
 
Figs, I too suspect the alternator. Do you by chance have a Plane Power? The AL60 rear bearing cavity has tended to enlarge, which would let the brush end of the rotor wobble, key symptom here being the beat in a narrow RPM range
 
Figs, I too suspect the alternator. Do you by chance have a Plane Power? The AL60 rear bearing cavity has tended to enlarge, which would let the brush end of the rotor wobble, key symptom here being the beat in a narrow RPM range

Yes I have the plane power 60A alternator, been on since 2008 (650 hours), all electrical indications have been fine (charge voltage etc). How do I check the bearing?
Figs
 
Yes I have the plane power 60A alternator, been on since 2008 (650 hours), all electrical indications have been fine (charge voltage etc). How do I check the bearing?
Figs

Run it up, then turn off the field power, then do it again. This would diagnose the alternator

To your question - - -remove the belt and wiggle hard on the pulley, DanH reported he had to put it into a vice, so it might be really stiff.
 
From the other side (it is a "headset problem of course"), does it do it with the mic disconnected?
 
Tried the recommended tests and it does not appear to be the alternator or the mic input, I talked to PS engineering and they suspect the audio input from the Aera 760 to the L/R music input on the PS3000 as the noise goes away when I select ISO and changes when I mute the music input.

Suspect the best solution would be to move the 760 audio to the PS3000 unswitched audio input and gang it with the Dynon audio, this is only mono but the 760 does not play music so it doesn't matter. With this setup I could switch off the intercom and still have audio alerts.

I remember a long thread about ganging mono and stereo audio inputs years ago so I will try to find that.
Appreciate all the inputs as always.
Figs
 
Noise source identified

After further testing PS engineering was correct the noise is coming from the Aera 760, some form of ground loop. They recommend installing a ground loop isolator which I have.
I did not have this noise with the previous Aera 796.
Figs
 
Noise problem solved

To close the loop on this thread, the problem was indeed noise being picked up from the aera 760 and it was due to me wiring the audio channel output from the aera 760 DB9 connector using 3 unshielded wires to a 1/8 audio jack to connect to the existing wiring from the prior 496/796 installation. On the advice of retired garmin expert Steve I rewired the audio channel to the intercom (without the socket/jack) using 3 wire shielded cable with the shielding grounded at the intercom and the system is now working fine.
Lesson learned about the importance of shielding as even though the wiring to the socket was not very long it did induce noise into the system.
Figs
 
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