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Troubleshooting radio whine/noise on Cessna 182P

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sacha

Joined: 04 Jan 2015
Posts: 15

Posted: Sun Nov 22, 2015 9:39 pm Post subject: Troubleshooting radio whine/noise on Cessna 182P

Hi Folks, 

it's been a while since I've posted - it's nice to be back.   I am the maintenance officer of a flying club which recently purchased a 1972 Cessna 182P and I've recently been quite busy... here is the story:



A week ago I was flying VFR at night and the alternator breaker popped in flight.  Luckily the battery had just been replaced and I was close to the airport so I was able to land without further incident.   



After I landed I reset the ALT breaker and noticed a whine in the headset and a low (12.9V bus voltage).  The whine varies in pitch with RPM and in volume with electrical load (eg. when I turn on the landing lights).



I replaced the alternator and that made no difference to either the whine or the low voltage.  I then replaced the alternator regulator and bus voltage is back up to 14.1V but the whine is unchanged.



Recent changes to the aircraft include:

- new Slick magnetos (a month ago, right after purchasing a/c)

- new battery (the day before the alternator failed), as previous battery appeared dead (had the charging system been broken for a while?)



It all sounds like it could be the result of some kind of ground loop but I can't quite see how that hypothesis fits with the history of the problems.



Does anyone have any ideas?



Sacha



PS. I've been reading the AeroElectric connection chapter 16 and based on that, here are the next tests I plan to do:

a.	Turn off alternator switch and see if noise disappears

b.	Disconnect antenna or turn down radio volume and see if noise disappears (means it’s entering the system through the antenna and not through the wiring)

c.	Check whether the phone and mic jacks are insulated from the (metal) airframe (but that's not something that recently changed, so unlikely to be the cause)

d.	If noise not generated by Alternator, suspect mags: 

   i. try turning off one mag in turn and see if noise disappears. 

   ii.	Try disconnecting the p-leads and see if noise disappears. 

   iii.	Otherwise spark plug harnesses might be suspect and should be tested for conductivity.

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Nov 23, 2015 6:57 am Post subject: Re: Troubleshooting radio whine/noise on Cessna 182P

The vast majority of electrical problems are caused by bad connections.  Checking each connection in both the positive and negative side of the circuits will only cost your time.  Take apart each connection, shine up the metal, apply a film of grease, and reassemble.  Also tug hard on each terminal and check for corrosion between wires and crimped terminals.

  Switches can also have internal corrosion.  Cycling them several times might clean the contacts.

_________________
Joe Gores

sacha

Joined: 04 Jan 2015
Posts: 15

Posted: Mon Nov 23, 2015 5:52 pm Post subject: Re: Troubleshooting radio whine/noise on Cessna 182P

Hi Joe,

thanks for that suggestion.  I now know that the noise comes from the Alternator and not the Mags.  I have a specific question:

Regarding the ground connections my A&P did the following tests:

- added a ground strap between the alternator and the engine crank case

- added a ground strap between the (rear-mounted) battery and the airframe

In neither case did the alternator whine disappear.  Are these tests sufficient to prove that these connections are not the cause of the whine?  

Sacha

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Nov 23, 2015 7:45 pm Post subject: Re: Troubleshooting radio whine/noise on Cessna 182P

 	  Quote: 	
		   Are these tests sufficient to prove that these connections are not the cause of the whine? 	


Probably.  There is also the connection between the engine case and the airframe.  And then there all of the connections on the positive side of the circuit.  Pay particular attention to the alternator and voltage regulator.

  Also check all audio input circuits like mics and intercom and music input.  Any audio circuit that gets amplified is vulnerable to noise.

_________________
Joe Gores

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Nov 23, 2015 8:35 pm Post subject: Re: Troubleshooting radio whine/noise on Cessna 182P

Microphone jacks should be insulated from the airframe. The coax should be grounded at the avionics end only.

_________________
Joe Gores

ceengland7(at)gmail.com
Guest

Posted: Mon Nov 23, 2015 9:22 pm Post subject: Troubleshooting radio whine/noise on Cessna 182P

On November 23, 2015 10:35:44 PM CST, user9253 <fransew(at)gmail.com> wrote:[quote]  ution -- 

 Sent from my Android device with K-9 Mail. Please excuse my brevity.

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Tue Nov 24, 2015 6:43 am Post subject: Re: Troubleshooting radio whine/noise on Cessna 182P

If no problem is found with the aircraft wiring or components, you might consider a filter (if legal on a 182).  This website tells how to make your own filter: http://www.sanantoniohams.org/tips/whine.htm

Or you can buy a pre-wound toroid (rated for load current) and add a capacitor at the avionics end.

Mouser and eBay sell both bare and pre-wound toroids.

Mouser part number: 704-CTX100-2-52LP-R

eBay item numbers: 400433590605, 191743622176, 370777920139

I am not necessarily recommending a filter but it might be worth a try if all else fails.

_________________
Joe Gores

sacha

Joined: 04 Jan 2015
Posts: 15

Posted: Tue Nov 24, 2015 7:02 am Post subject: Re: Troubleshooting radio whine/noise on Cessna 182P

Thanks.  There is already an inductive and a capacitive noise filter on the 182.  



What I'm thinking of though is: two weeks ago (before the ALT breaker popped in flight) everything was fine.  So that breaker popping and then the noise appearing as soon as I reset the breaker on the ground must mean that *SOMETHING* has changed: it's unlikely to be the mic/phone jacks so I'm wondering what it could be that was damaged/changed:

- could it be that the noise filters were fried by an over-voltage event?  (but if it was an overvoltage event, the ALT reg CB should have popped, not the ALT CB).



There were actually two problems: 

- low bus voltage

- noise

Replacing the alternator solved neither.  On Friday, my A&P made a temporary installation of a new voltage regulator and that solved the low voltage problem.  But that installation did not allow the alternator to go offline when the ALT rocker switch was turned off.  Yesterday, he finished the installation and verified that when the ALT is turned off, the noise disapears.  But the interesting thing is that he mentioned that the bus voltage is now 13.5V vs 14.1V on Friday.  So I'm now suspecting that the ALT rocker switch is offering some unusual resistance.

Could that have been caused by whatever caused the ALT breaker to pop?



I guess the next step is to bypass the ALT rocker switch and see if at least the bus voltage returns to 14.1V.  Thoughts?



The electrical schematic is on p.18 (numbered 2-4) of http://www.t-craft.org/Fleet/C182P-POH.pdf

jan(at)CLAVER.DEMON.CO.UK
Guest

Posted: Tue Nov 24, 2015 7:27 am Post subject: Troubleshooting radio whine/noise on Cessna 182P

Stupid question maybe but is the new voltage regulator identical to the old unit ? 



All the best



Jan



 	  Quote: 	
		   On Nov 24, 2015, at 15:02, sacha <uuccio(at)gmail.com> wrote:

 

 

 

 Thanks.  There is already an inductive and a capacitive noise filter on the 182.  

 

 What I'm thinking of though is: two weeks ago (before the ALT breaker popped in flight) everything was fine.  So that breaker popping and then the noise appearing as soon as I reset the breaker on the ground must mean that *SOMETHING* has changed: it's unlikely to be the mic/phone jacks so I'm wondering what it could be that was damaged/changed:

 - could it be that the noise filters were fried by an over-voltage event?  (but if it was an overvoltage event, the ALT reg CB should have popped, not the ALT CB).

 

 There were actually two problems: 

 - low bus voltage

 - noise

 Replacing the alternator solved neither.  On Friday, my A&P made a temporary installation of a new voltage regulator and that solved the low voltage problem.  But that installation did not allow the alternator to go offline when the ALT rocker switch was turned off.  Yesterday, he finished the installation and verified that when the ALT is turned off, the noise disapears.  But the interesting thing is that he mentioned that the bus voltage is now 13.5V vs 14.1V on Friday.  So I'm now suspecting that the ALT rocker switch is offering some unusual resistance.

 Could that have been caused by whatever caused the ALT breaker to pop?

 

 I guess the next step is to bypass the ALT rocker switch and see if at least the bus voltage returns to 14.1V.  Thoughts?

 

 The electrical schematic is on p.18 (numbered 2-4) of http://www.t-craft.org/Fleet/C182P-POH.pdf

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=450095#450095

sacha

Joined: 04 Jan 2015
Posts: 15

Posted: Tue Nov 24, 2015 7:33 am Post subject: Re: Troubleshooting radio whine/noise on Cessna 182P

Hi Jan

No it isn't. The old one is a Ford. The new one a Plane Power regulator. 

Can you explain why you're asking?

Sacha

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Tue Nov 24, 2015 8:42 am Post subject: Re: Troubleshooting radio whine/noise on Cessna 182P

Using the voltage regulator CASE as a reference point (not the airframe or battery negative), measure the voltage on the regulator "sense" terminal.  Is it the same as battery voltage?  If not, find out where the voltage is being dropped.

  Over-voltage can destroy capacitors.  The capacitors could be tested to make sure they are OK.

_________________
Joe Gores

neal.george(at)gmail.com
Guest

Posted: Tue Nov 24, 2015 5:18 pm Post subject: Troubleshooting radio whine/noise on Cessna 182P

I don't suggest that it is contributing to the noise problem, but I DO suspect it is old and has tarnished / corroded contacts that add resistance to the circuit. Could contribute to the voltage sensing and regulation issues...



Neal George

Sent from my iPhone



 	  Quote: 	
		   On Nov 24, 2015, at 6:34 PM, sacha <uuccio(at)gmail.com> wrote:

 

 

 

 Neal, 

 thank you for that.  I only just saw your post.  It looks like the issue with the regulator has been sorted out.  I'm guessing the master switch is fine too but I'll bypass it in a test just to be sure.

 Sacha

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=450197#450197

sacha

Joined: 04 Jan 2015
Posts: 15

Posted: Tue Nov 24, 2015 6:14 pm Post subject: Re: Troubleshooting radio whine/noise on Cessna 182P

Good point. It's not a big ticket item (thought $40 seems a lot for two switches) so I guess I ought to swap it out.

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