Radio noise

by William Campbell in 912 / 914 Technical Questions 8 years ago

I need your help. I have a 912UL 80hp rotax of the 2007 vintage with 350hrs. About 2 months ago I started picking up a clicking noise in my headset with the com radio on. I have a MicroAir 760 com. It started intermittently at low RPM's and gradually increased to doing it at cruise RPM. Although it sometimes stops entirely for no reason for a moment of two, :( it is an absolute nuisance. I thought it was ignition noise at first but it does not change on the ignition run up check. Further research let me to believe it is noise from the charging system as I can hear it after shutting off the ignitions with the key still on as it spins to a stop. Nothing has been changed or added to the airplane during this time

I see there is some sort of capacitor below the regulator mounted on the firewall on the pilot side. I need to get this resolved. Does anyone have any ideas or solutions.

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Re: Radio noise

by Garrett Wysocki » 8 years ago

Garrett Wysocki

1 572 1.45k

Check the charge circuit connections and capacitor. Mine went bad after overloading the charge circuit.

Thank you said by: William Campbell

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Re: Radio noise

by Ian Rees » 8 years ago

Ian Rees

6 42 0

You could check a number of things.

a) The rectifier/regulator capacitor. Check for leakage around the case. Any fluid, means replace the cap. Wash your hands of any fluid.
spec's on the cap are in the Rotax manual.
b) Assuming you have a intercomm and headset system (Lynx, Flycomm or other type) connected to the Microair 760, check all power supply wires are secure between all of these items. Some systems have 12VDC power filters to filter the incoming 12V, check it.
c) Measure the 12V supply to the radio gear, an oscilloscope will show how clean it is, otherwise check with a multi meter.
d) After you check everything, let us know what you find.

If after you do all checks and measurements and can't find anything, I suggest you get an electrical or electronics person to have a look.
If you still can't find the fault, suggest to borrow a reg/rectifier and do a swap test. Only swap one thing at a time. Cap first, re-test, etc.

Good luck.

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Re: Radio noise

by Alan Arnold » 8 years ago

Alan Arnold

20 188 145

A primary suspect in radio noise is poor grounds. They slowly loosen and/or corrode.

Alan

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Re: Radio noise

by William Campbell » 8 years ago

William Campbell

15 25 43

This message is in response to the clicking noise heard in my headset that began months ago. I speculated it was from the charging system as it would continue once the ignitions were shut off and the engine spun down. I was also showing around 12.1 Volts or less on my EIS instrument. I made sure the wires on the capacitor were clean. The capacitor was not leaking. I added additional grounds to the Voltage regulator and shielded wiring harness going to the cabin. I checked all the small wires to the ignitions and the I even tried another Voltage regulator and nothing changed.

My mechanic found the problem. I was the problem!!. All winter I was using a battery tender on the battery to insure a good spin for starting my 80HP 912UL. My flights were not over two hours total and the plane went back on the battery tender at the end of each flight. I had my mechanic fly in and do the annual on my engine. He tried another voltage regulator without any success. He then started checking voltages by removing he multi pin plug that connects to the voltage regulator. Here he found issues with Zero Voltage on some of the pins.

Long and short is he found the fuse to the charging system blown. New fuse installed and my original regulator re-installed. Started the engine and checked the EIS system and the Voltage increased to 13.8 Volts and the clicking noise in my headset was gone. The fuse in this airplane is one of the flat automotive type fuses. One of the 2 legs came lose and caused the fuse to open.

I thought the battery was staying charged enough in flight and the battery tender was maintaining the charge between flights. My lesson: Check the simplest of things first.

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Radio noise

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